Introduce StyleManager

A Page now has a StyleManager. The StyleManager currently answers two questions:
1 - Is an element hidden
2 - Does an element have pointer-events == none

This is used in calls such as element.checkVisibility which, on some pages, can
be called tens of thousands of times (often through other methods, like
element.getBoundingClientRect). This _can_ be a bottleneck.

The StyleManager keeps a list of rules. The rules include the selector,
specificity, and properties that we care about. Rules in a stylesheet that
contain no properties of interest are ignored. This is the first and likely
most significant optimization. Presumably, most CSS rules don't have a
display/visibility/opacity or pointer-events property.

The list is rules is cached until stylesheets are modified or delete. When this
happens, the StyleManager is flagged as "dirty" and rebuilt on-demand in the
next query.  This is our second major optimization.

For now, to check if an element is visible, we still need to scan all rules.
But having a pre-build subset of all the rules is a first step.

The next step might be to optimize the matching, or possibly optimizing common
cases (e.g. id and/or simple class selector)

src/SemanticTree.zig

@@ -45,8 +45,9 @@ pub fn jsonStringify(self: @This(), jw: *std.json.Stringify) error{WriteFailed}!
         log.err(.app, "listener map failed", .{ .err = err });
         return error.WriteFailed;
     };
-    var css_cache: Element.CssCache = .empty;
-    self.walk(self.dom_node, &xpath_buffer, null, &visitor, 1, listener_targets, &css_cache) catch |err| {
+    var visibility_cache: Element.VisibilityCache = .empty;
+    var pointer_events_cache: Element.PointerEventsCache = .empty;
+    self.walk(self.dom_node, &xpath_buffer, null, &visitor, 1, listener_targets, &visibility_cache, &pointer_events_cache) catch |err| {
         log.err(.app, "semantic tree json dump failed", .{ .err = err });
         return error.WriteFailed;
     };
@@ -59,8 +60,9 @@ pub fn textStringify(self: @This(), writer: *std.Io.Writer) error{WriteFailed}!v
         log.err(.app, "listener map failed", .{ .err = err });
         return error.WriteFailed;
     };
-    var css_cache: Element.CssCache = .empty;
-    self.walk(self.dom_node, &xpath_buffer, null, &visitor, 1, listener_targets, &css_cache) catch |err| {
+    var visibility_cache: Element.VisibilityCache = .empty;
+    var pointer_events_cache: Element.PointerEventsCache = .empty;
+    self.walk(self.dom_node, &xpath_buffer, null, &visitor, 1, listener_targets, &visibility_cache, &pointer_events_cache) catch |err| {
         log.err(.app, "semantic tree text dump failed", .{ .err = err });
         return error.WriteFailed;
     };
@@ -84,7 +86,7 @@ const NodeData = struct {
     node_name: []const u8,
 };
 
-fn walk(self: @This(), node: *Node, xpath_buffer: *std.ArrayList(u8), parent_name: ?[]const u8, visitor: anytype, index: usize, listener_targets: interactive.ListenerTargetMap, css_cache: ?*Element.CssCache) !void {
+fn walk(self: @This(), node: *Node, xpath_buffer: *std.ArrayList(u8), parent_name: ?[]const u8, visitor: anytype, index: usize, listener_targets: interactive.ListenerTargetMap, visibility_cache: ?*Element.VisibilityCache, pointer_events_cache: ?*Element.PointerEventsCache) !void {
     // 1. Skip non-content nodes
     if (node.is(Element)) |el| {
         const tag = el.getTag();
@@ -94,7 +96,7 @@ fn walk(self: @This(), node: *Node, xpath_buffer: *std.ArrayList(u8), parent_nam
         if (tag == .datalist or tag == .option or tag == .optgroup) return;
 
         // Check visibility using the engine's checkVisibility which handles CSS display: none
-        if (!el.checkVisibilityCached(css_cache, self.page)) {
+        if (!el.checkVisibilityCached(visibility_cache, self.page)) {
             return;
         }
 
@@ -135,7 +137,7 @@ fn walk(self: @This(), node: *Node, xpath_buffer: *std.ArrayList(u8), parent_nam
         }
 
         if (el.is(Element.Html)) |html_el| {
-            if (interactive.classifyInteractivity(self.page, el, html_el, listener_targets, css_cache) != null) {
+            if (interactive.classifyInteractivity(self.page, el, html_el, listener_targets, pointer_events_cache) != null) {
                 is_interactive = true;
             }
         }
@@ -215,7 +217,7 @@ fn walk(self: @This(), node: *Node, xpath_buffer: *std.ArrayList(u8), parent_nam
             }
             gop.value_ptr.* += 1;
 
-            try self.walk(child, xpath_buffer, name, visitor, gop.value_ptr.*, listener_targets, css_cache);
+            try self.walk(child, xpath_buffer, name, visitor, gop.value_ptr.*, listener_targets, visibility_cache, pointer_events_cache);
         }
     }
 

src/browser/Page.zig

@@ -35,6 +35,7 @@ const Factory = @import("Factory.zig");
 const Session = @import("Session.zig");
 const EventManager = @import("EventManager.zig");
 const ScriptManager = @import("ScriptManager.zig");
+const StyleManager = @import("StyleManager.zig");
 
 const Parser = @import("parser/Parser.zig");
 
@@ -143,6 +144,7 @@ _blob_urls: std.StringHashMapUnmanaged(*Blob) = .{},
 /// A call to `documentIsComplete` (which calls `_documentIsComplete`) resets it.
 _to_load: std.ArrayList(*Element.Html) = .{},
 
+_style_manager: StyleManager,
 _script_manager: ScriptManager,
 
 // List of active live ranges (for mutation updates per DOM spec)
@@ -268,6 +270,7 @@ pub fn init(self: *Page, frame_id: u32, session: *Session, parent: ?*Page) !void
         ._factory = factory,
         ._pending_loads = 1, // always 1 for the ScriptManager
         ._type = if (parent == null) .root else .frame,
+        ._style_manager = undefined,
         ._script_manager = undefined,
         ._event_manager = EventManager.init(session.page_arena, self),
     };
@@ -297,6 +300,9 @@ pub fn init(self: *Page, frame_id: u32, session: *Session, parent: ?*Page) !void
         ._visual_viewport = visual_viewport,
     });
 
+    self._style_manager = try StyleManager.init(self);
+    errdefer self._style_manager.deinit();
+
     const browser = session.browser;
     self._script_manager = ScriptManager.init(browser.allocator, browser.http_client, self);
     errdefer self._script_manager.deinit();
@@ -353,6 +359,7 @@ pub fn deinit(self: *Page, abort_http: bool) void {
     }
 
     self._script_manager.deinit();
+    self._style_manager.deinit();
 
     session.releaseArena(self.call_arena);
 }
@@ -2538,6 +2545,17 @@ pub fn removeNode(self: *Page, parent: *Node, child: *Node, opts: RemoveNodeOpts
         }
 
         Element.Html.Custom.invokeDisconnectedCallbackOnElement(el, self);
+
+        // If a <style> element is being removed, remove its sheet from the list
+        if (el.is(Element.Html.Style)) |style| {
+            if (style._sheet) |sheet| {
+                if (self.document._style_sheets) |sheets| {
+                    sheets.remove(sheet);
+                }
+                style._sheet = null;
+            }
+            self._style_manager.sheetModified();
+        }
     }
 }
 

src/browser/StyleManager.zig

@@ -0,0 +1,572 @@
+// Copyright (C) 2023-2026  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.io>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+
+const log = @import("../log.zig");
+const String = @import("../string.zig").String;
+
+const Page = @import("Page.zig");
+
+const CssParser = @import("css/Parser.zig");
+const Element = @import("webapi/Element.zig");
+
+const Selector = @import("webapi/selector/Selector.zig");
+const SelectorParser = @import("webapi/selector/Parser.zig");
+const SelectorList = @import("webapi/selector/List.zig");
+
+const CSSStyleRule = @import("webapi/css/CSSStyleRule.zig");
+const CSSStyleSheet = @import("webapi/css/CSSStyleSheet.zig");
+const CSSStyleProperties = @import("webapi/css/CSSStyleProperties.zig");
+const CSSStyleProperty = @import("webapi/css/CSSStyleDeclaration.zig").Property;
+
+const Allocator = std.mem.Allocator;
+
+pub const VisibilityCache = std.AutoHashMapUnmanaged(*Element, bool);
+pub const PointerEventsCache = std.AutoHashMapUnmanaged(*Element, bool);
+
+// Tracks visibility-relevant CSS rules from <style> elements.
+const StyleManager = @This();
+
+page: *Page,
+
+arena: Allocator,
+
+// Sorted in document order. Only ryles that we care about (display, visibility, ...)
+rules: std.ArrayList(VisibilityRule) = .empty,
+
+// When true, rules need to be rebuilt
+dirty: bool = false,
+
+pub fn init(page: *Page) !StyleManager {
+    return .{
+        .page = page,
+        .arena = try page.getArena(.{ .debug = "StyleManager" }),
+    };
+}
+
+pub fn deinit(self: *StyleManager) void {
+    self.page.releaseArena(self.arena);
+}
+
+pub fn sheetAdded(self: *StyleManager, sheet: *CSSStyleSheet) !void {
+    const css_rules = sheet._css_rules orelse return;
+
+    for (css_rules._rules.items) |rule| {
+        const style_rule = rule.is(CSSStyleRule) orelse continue;
+        try self.addRule(style_rule);
+    }
+}
+
+pub fn sheetRemoved(self: *StyleManager) void {
+    self.dirty = true;
+}
+
+pub fn sheetModified(self: *StyleManager) void {
+    self.dirty = true;
+}
+
+/// Rebuilds the rule list from all document stylesheets.
+/// Called lazily when dirty flag is set and rules are needed.
+fn rebuildIfDirty(self: *StyleManager) !void {
+    if (!self.dirty) {
+        return;
+    }
+
+    self.dirty = false;
+    const item_count = self.rules.items.len;
+
+    const arena: *std.heap.ArenaAllocator = @ptrCast(@alignCast(self.arena.ptr));
+    _ = arena.reset(.retain_capacity);
+
+    self.rules = try .initCapacity(self.arena, item_count);
+    const sheets = self.page.document._style_sheets orelse return;
+    for (sheets._sheets.items) |sheet| {
+        self.sheetAdded(sheet) catch |err| {
+            log.err(.browser, "StyleManager sheetAdded", .{ .err = err });
+            return err;
+        };
+    }
+}
+
+// Check if an element is hidden based on options.
+// By default only checks display:none.
+// Walks up the tree to check ancestors.
+pub fn isHidden(self: *StyleManager, el: *Element, cache: ?*VisibilityCache, options: CheckVisibilityOptions) bool {
+    var current: ?*Element = el;
+
+    while (current) |elem| {
+        // Check cache first (only when checking all properties for caching consistency)
+        if (cache) |c| {
+            if (c.get(elem)) |hidden| {
+                if (hidden) {
+                    return true;
+                }
+                current = elem.parentElement();
+                continue;
+            }
+        }
+
+        const hidden = self.isElementHidden(elem, options);
+
+        // Store in cache
+        if (cache) |c| {
+            c.put(self.page.call_arena, elem, hidden) catch {};
+        }
+
+        if (hidden) {
+            return true;
+        }
+        current = elem.parentElement();
+    }
+
+    return false;
+}
+
+/// Check if a single element (not ancestors) is hidden.
+fn isElementHidden(self: *StyleManager, el: *Element, options: CheckVisibilityOptions) bool {
+    // Track best match per property (value + specificity)
+    // Initialize spec to INLINE_SPECIFICITY for properties we don't care about - this makes
+    // the loop naturally skip them since no stylesheet rule can have specificity >= INLINE_SPECIFICITY
+    var display_none: ?bool = null;
+    var display_spec: u32 = 0;
+
+    var visibility_hidden: ?bool = null;
+    var visibility_spec: u32 = 0;
+
+    var opacity_zero: ?bool = null;
+    var opacity_spec: u32 = 0;
+
+    // Check inline styles FIRST - they use INLINE_SPECIFICITY so no stylesheet can beat them
+    if (getInlineStyleProperty(el, comptime .wrap("display"), self.page)) |property| {
+        if (property._value.eql(comptime .wrap("none"))) {
+            return true; // Early exit for hiding value
+        }
+        display_none = false;
+        display_spec = INLINE_SPECIFICITY;
+    }
+
+    if (options.check_visibility) {
+        if (getInlineStyleProperty(el, comptime .wrap("visibility"), self.page)) |property| {
+            if (property._value.eql(comptime .wrap("hidden")) or property._value.eql(comptime .wrap("collapse"))) {
+                return true;
+            }
+            visibility_hidden = false;
+            visibility_spec = INLINE_SPECIFICITY;
+        }
+    } else {
+        // This can't be beat. Setting this means that, when checking rules
+        // we no longer have to check if options.check_visibility is enabled.
+        // We can just compare the specificity.
+        visibility_spec = INLINE_SPECIFICITY;
+    }
+
+    if (options.check_opacity) {
+        if (getInlineStyleProperty(el, comptime .wrap("opacity"), self.page)) |property| {
+            if (property._value.eql(comptime .wrap("0"))) {
+                return true;
+            }
+            opacity_zero = false;
+            opacity_spec = INLINE_SPECIFICITY;
+        }
+    } else {
+        opacity_spec = INLINE_SPECIFICITY;
+    }
+
+    if (display_spec == INLINE_SPECIFICITY and visibility_spec == INLINE_SPECIFICITY and opacity_spec == INLINE_SPECIFICITY) {
+        return false;
+    }
+
+    self.rebuildIfDirty() catch return false;
+
+    for (self.rules.items) |rule| {
+        // Skip rules that can't possibly update any property we care about
+        const dominated = (rule.props.display_none == null or rule.specificity < display_spec) and
+            (rule.props.visibility_hidden == null or rule.specificity < visibility_spec) and
+            (rule.props.opacity_zero == null or rule.specificity < opacity_spec);
+        if (dominated) continue;
+
+        if (matchesSelector(el, rule.selector, self.page)) {
+            if (rule.props.display_none != null and rule.specificity >= display_spec) {
+                display_none = rule.props.display_none;
+                display_spec = rule.specificity;
+            }
+            if (rule.props.visibility_hidden != null and rule.specificity >= visibility_spec) {
+                visibility_hidden = rule.props.visibility_hidden;
+                visibility_spec = rule.specificity;
+            }
+            if (rule.props.opacity_zero != null and rule.specificity >= opacity_spec) {
+                opacity_zero = rule.props.opacity_zero;
+                opacity_spec = rule.specificity;
+            }
+        }
+    }
+
+    return (display_none orelse false) or (visibility_hidden orelse false) or (opacity_zero orelse false);
+}
+
+/// Check if an element has pointer-events:none.
+/// Checks inline style first - if set, skips stylesheet lookup.
+/// Walks up the tree to check ancestors.
+pub fn hasPointerEventsNone(self: *StyleManager, el: *Element, cache: ?*PointerEventsCache) bool {
+    var current: ?*Element = el;
+
+    while (current) |elem| {
+        // Check cache first
+        if (cache) |c| {
+            if (c.get(elem)) |pe_none| {
+                if (pe_none) return true;
+                current = elem.parentElement();
+                continue;
+            }
+        }
+
+        const pe_none = self.elementHasPointerEventsNone(elem);
+
+        // Store in cache
+        if (cache) |c| {
+            c.put(self.page.call_arena, elem, pe_none) catch {};
+        }
+
+        if (pe_none) return true;
+        current = elem.parentElement();
+    }
+
+    return false;
+}
+
+/// Check if a single element (not ancestors) has pointer-events:none.
+fn elementHasPointerEventsNone(self: *StyleManager, el: *Element) bool {
+    const page = self.page;
+
+    var result: ?bool = null;
+    var best_spec: u32 = 0;
+
+    // Check inline style first
+    if (getInlineStyleProperty(el, .wrap("pointer-events"), page)) |property| {
+        if (property._value.eql(comptime .wrap("none"))) {
+            return true;
+        }
+        // Inline set to non-none - no stylesheet can override
+        return false;
+    }
+
+    // Check stylesheet rules
+    self.rebuildIfDirty() catch return false;
+
+    for (self.rules.items) |rule| {
+        if (rule.props.pointer_events_none == null or rule.specificity < best_spec) {
+            continue;
+        }
+
+        if (matchesSelector(el, rule.selector, page)) {
+            result = rule.props.pointer_events_none;
+            best_spec = rule.specificity;
+        }
+    }
+
+    return result orelse false;
+}
+
+// Extracts visibility-relevant rules from a CSS rule.
+// Creates one VisibilityRule per selector (not per selector list) so each has correct specificity.
+fn addRule(self: *StyleManager, style_rule: *CSSStyleRule) !void {
+    const selector_text = style_rule._selector_text;
+    if (selector_text.len == 0) {
+        return;
+    }
+
+    // Check if the rule has visibility-relevant properties
+    const style = style_rule._style orelse return;
+    const props = extractVisibilityProperties(style);
+    if (!props.isRelevant()) {
+        return;
+    }
+
+    // Parse the selector list
+    const selectors = SelectorParser.parseList(self.arena, selector_text, self.page) catch return;
+    if (selectors.len == 0) {
+        return;
+    }
+
+    // Create one rule per selector - each has its own specificity
+    // e.g., "#id, .class { display: none }" becomes two rules with different specificities
+    for (selectors) |selector| {
+        const rule = VisibilityRule{
+            .props = props,
+            .selector = selector,
+            .specificity = computeSpecificity(selector),
+        };
+        try self.rules.append(self.arena, rule);
+    }
+}
+
+/// Extracts visibility-relevant properties from a style declaration.
+fn extractVisibilityProperties(style: *CSSStyleProperties) VisibilityProperties {
+    var props = VisibilityProperties{};
+    const decl = style.asCSSStyleDeclaration();
+
+    if (decl.findProperty(comptime .wrap("display"))) |property| {
+        props.display_none = property._value.eql(comptime .wrap("none"));
+    }
+
+    if (decl.findProperty(comptime .wrap("visibility"))) |property| {
+        props.visibility_hidden = property._value.eql(comptime .wrap("hidden")) or property._value.eql(comptime .wrap("collapse"));
+    }
+
+    if (decl.findProperty(comptime .wrap("opacity"))) |property| {
+        props.opacity_zero = property._value.eql(comptime .wrap("0"));
+    }
+
+    if (decl.findProperty(.wrap("pointer-events"))) |property| {
+        props.pointer_events_none = property._value.eql(comptime .wrap("none"));
+    }
+
+    return props;
+}
+
+// Computes CSS specificity for a selector.
+// Returns packed value: (id_count << 20) | (class_count << 10) | element_count
+pub fn computeSpecificity(selector: Selector.Selector) u32 {
+    var ids: u32 = 0;
+    var classes: u32 = 0; // includes classes, attributes, pseudo-classes
+    var elements: u32 = 0; // includes elements, pseudo-elements
+
+    // Count specificity for first compound
+    countCompoundSpecificity(selector.first, &ids, &classes, &elements);
+
+    // Count specificity for subsequent segments
+    for (selector.segments) |segment| {
+        countCompoundSpecificity(segment.compound, &ids, &classes, &elements);
+    }
+
+    // Pack into single u32: (ids << 20) | (classes << 10) | elements
+    // This gives us 10 bits each, supporting up to 1023 of each type
+    return (ids << 20) | (classes << 10) | elements;
+}
+
+fn countCompoundSpecificity(compound: Selector.Compound, ids: *u32, classes: *u32, elements: *u32) void {
+    for (compound.parts) |part| {
+        switch (part) {
+            .id => ids.* += 1,
+            .class => classes.* += 1,
+            .tag, .tag_name => elements.* += 1,
+            .universal => {}, // zero specificity
+            .attribute => classes.* += 1,
+            .pseudo_class => |pc| {
+                switch (pc) {
+                    // :where() has zero specificity
+                    .where => {},
+                    // :not(), :is(), :has() take specificity of their most specific argument
+                    .not, .is, .has => |nested| {
+                        var max_nested: u32 = 0;
+                        for (nested) |nested_sel| {
+                            const spec = computeSpecificity(nested_sel);
+                            if (spec > max_nested) max_nested = spec;
+                        }
+                        // Unpack and add to our counts
+                        ids.* += (max_nested >> 20) & 0x3FF;
+                        classes.* += (max_nested >> 10) & 0x3FF;
+                        elements.* += max_nested & 0x3FF;
+                    },
+                    // All other pseudo-classes count as class-level specificity
+                    else => classes.* += 1,
+                }
+            },
+        }
+    }
+}
+
+fn matchesSelector(el: *Element, selector: Selector.Selector, page: *Page) bool {
+    const node = el.asNode();
+    return SelectorList.matches(node, selector, node, page);
+}
+
+const VisibilityProperties = struct {
+    display_none: ?bool = null,
+    visibility_hidden: ?bool = null,
+    opacity_zero: ?bool = null,
+    pointer_events_none: ?bool = null,
+
+    // returne true if any field in VisibilityProperties is not null
+    fn isRelevant(self: VisibilityProperties) bool {
+        return self.display_none != null or
+            self.visibility_hidden != null or
+            self.opacity_zero != null or
+            self.pointer_events_none != null;
+    }
+};
+
+const VisibilityRule = struct {
+    selector: Selector.Selector, // Single selector, not a list
+    props: VisibilityProperties,
+
+    // Packed specificity: (id_count << 20) | (class_count << 10) | element_count
+    // Document order is implicit in array position - equal specificity with later position wins
+    specificity: u32,
+};
+
+const CheckVisibilityOptions = struct {
+    check_opacity: bool = false,
+    check_visibility: bool = false,
+};
+
+// Inline styles always win over stylesheets - use max u32 as sentinel
+const INLINE_SPECIFICITY: u32 = std.math.maxInt(u32);
+
+fn getInlineStyleProperty(el: *Element, property_name: String, page: *Page) ?*CSSStyleProperty {
+    const style = el.getOrCreateStyle(page) catch |err| {
+        log.err(.browser, "StyleManager getOrCreateStyle", .{ .err = err });
+        return null;
+    };
+    return style.asCSSStyleDeclaration().findProperty(property_name);
+}
+
+const testing = @import("../testing.zig");
+test "StyleManager: computeSpecificity: element selector" {
+    // div -> (0, 0, 1)
+    const selector = Selector.Selector{
+        .first = .{ .parts = &.{.{ .tag = .div }} },
+        .segments = &.{},
+    };
+    try testing.expectEqual(1, computeSpecificity(selector));
+}
+
+test "StyleManager: computeSpecificity: class selector" {
+    // .foo -> (0, 1, 0)
+    const selector = Selector.Selector{
+        .first = .{ .parts = &.{.{ .class = "foo" }} },
+        .segments = &.{},
+    };
+    try testing.expectEqual(1 << 10, computeSpecificity(selector));
+}
+
+test "StyleManager: computeSpecificity: id selector" {
+    // #bar -> (1, 0, 0)
+    const selector = Selector.Selector{
+        .first = .{ .parts = &.{.{ .id = "bar" }} },
+        .segments = &.{},
+    };
+    try testing.expectEqual(1 << 20, computeSpecificity(selector));
+}
+
+test "StyleManager: computeSpecificity: combined selector" {
+    // div.foo#bar -> (1, 1, 1)
+    const selector = Selector.Selector{
+        .first = .{ .parts = &.{
+            .{ .tag = .div },
+            .{ .class = "foo" },
+            .{ .id = "bar" },
+        } },
+        .segments = &.{},
+    };
+    try testing.expectEqual((1 << 20) | (1 << 10) | 1, computeSpecificity(selector));
+}
+
+test "StyleManager: computeSpecificity: universal selector" {
+    // * -> (0, 0, 0)
+    const selector = Selector.Selector{
+        .first = .{ .parts = &.{.universal} },
+        .segments = &.{},
+    };
+    try testing.expectEqual(0, computeSpecificity(selector));
+}
+
+test "StyleManager: computeSpecificity: multiple classes" {
+    // .a.b.c -> (0, 3, 0)
+    const selector = Selector.Selector{
+        .first = .{ .parts = &.{
+            .{ .class = "a" },
+            .{ .class = "b" },
+            .{ .class = "c" },
+        } },
+        .segments = &.{},
+    };
+    try testing.expectEqual(3 << 10, computeSpecificity(selector));
+}
+
+test "StyleManager: computeSpecificity: descendant combinator" {
+    // div span -> (0, 0, 2)
+    const selector = Selector.Selector{
+        .first = .{ .parts = &.{.{ .tag = .div }} },
+        .segments = &.{
+            .{ .combinator = .descendant, .compound = .{ .parts = &.{.{ .tag = .span }} } },
+        },
+    };
+    try testing.expectEqual(2, computeSpecificity(selector));
+}
+
+test "StyleManager: computeSpecificity: :where() has zero specificity" {
+    // :where(.foo) -> (0, 0, 0) regardless of what's inside
+    const inner_selector = Selector.Selector{
+        .first = .{ .parts = &.{.{ .class = "foo" }} },
+        .segments = &.{},
+    };
+    const selector = Selector.Selector{
+        .first = .{ .parts = &.{
+            .{ .pseudo_class = .{ .where = &.{inner_selector} } },
+        } },
+        .segments = &.{},
+    };
+    try testing.expectEqual(0, computeSpecificity(selector));
+}
+
+test "StyleManager: computeSpecificity: :not() takes inner specificity" {
+    // :not(.foo) -> (0, 1, 0) - takes specificity of .foo
+    const inner_selector = Selector.Selector{
+        .first = .{ .parts = &.{.{ .class = "foo" }} },
+        .segments = &.{},
+    };
+    const selector = Selector.Selector{
+        .first = .{ .parts = &.{
+            .{ .pseudo_class = .{ .not = &.{inner_selector} } },
+        } },
+        .segments = &.{},
+    };
+    try testing.expectEqual(1 << 10, computeSpecificity(selector));
+}
+
+test "StyleManager: computeSpecificity: :is() takes most specific inner" {
+    // :is(.foo, #bar) -> (1, 0, 0) - takes the most specific (#bar)
+    const class_selector = Selector.Selector{
+        .first = .{ .parts = &.{.{ .class = "foo" }} },
+        .segments = &.{},
+    };
+    const id_selector = Selector.Selector{
+        .first = .{ .parts = &.{.{ .id = "bar" }} },
+        .segments = &.{},
+    };
+    const selector = Selector.Selector{
+        .first = .{ .parts = &.{
+            .{ .pseudo_class = .{ .is = &.{ class_selector, id_selector } } },
+        } },
+        .segments = &.{},
+    };
+    try testing.expectEqual(1 << 20, computeSpecificity(selector));
+}
+
+test "StyleManager: computeSpecificity: pseudo-class (general)" {
+    // :hover -> (0, 1, 0) - pseudo-classes count as class-level
+    const selector = Selector.Selector{
+        .first = .{ .parts = &.{
+            .{ .pseudo_class = .hover },
+        } },
+        .segments = &.{},
+    };
+    try testing.expectEqual(1 << 10, computeSpecificity(selector));
+}

src/browser/interactive.zig

@@ -133,7 +133,7 @@ pub fn collectInteractiveElements(
     // so classify and getListenerTypes are both O(1) per element.
     const listener_targets = try buildListenerTargetMap(page, arena);
 
-    var css_cache: Element.CssCache = .empty;
+    var css_cache: Element.PointerEventsCache = .empty;
 
     var results: std.ArrayList(InteractiveElement) = .empty;
 
@@ -216,7 +216,7 @@ pub fn classifyInteractivity(
     el: *Element,
     html_el: *Element.Html,
     listener_targets: ListenerTargetMap,
-    cache: ?*Element.CssCache,
+    cache: ?*Element.PointerEventsCache,
 ) ?InteractivityType {
     if (el.hasPointerEventsNone(cache, page)) return null;
 

src/browser/tests/css.html

@@ -77,33 +77,3 @@
     testing.expectEqual('\uFFFDabc', CSS.escape('\x00abc'));
   }
 </script>
-
-<script id="checkVisibility">
-  {
-    const el = document.createElement("div");
-    document.documentElement.appendChild(el);
-    testing.expectEqual(true, el.checkVisibility());
-
-    el.style.display = "none";
-    testing.expectEqual(false, el.checkVisibility());
-
-    el.style.display = "block";
-    testing.expectEqual(true, el.checkVisibility());
-
-    el.style.visibility = "hidden";
-    testing.expectEqual(false, el.checkVisibility());
-
-    el.style.visibility = "collapse";
-    testing.expectEqual(false, el.checkVisibility());
-
-    el.style.visibility = "visible";
-    testing.expectEqual(true, el.checkVisibility());
-
-    el.style.opacity = "0";
-    testing.expectEqual(false, el.checkVisibility());
-
-    el.style.opacity = "1";
-    testing.expectEqual(true, el.checkVisibility());
-    document.documentElement.removeChild(el);
-  }
-</script>

src/browser/tests/element/check_visibility.html

@@ -0,0 +1,226 @@
+<!DOCTYPE html>
+<script src="../testing.js"></script>
+<body></body>
+
+<!-
+<script id="inline_display_none">
+  {
+    const el = document.createElement("div");
+    document.body.appendChild(el);
+    testing.expectEqual(true, el.checkVisibility());
+
+    el.style.display = "none";
+    testing.expectEqual(false, el.checkVisibility());
+
+    el.style.display = "block";
+    testing.expectEqual(true, el.checkVisibility());
+
+    el.remove();
+  }
+</script>
+
+<script id="inline_visibility_hidden">
+  {
+    const el = document.createElement("div");
+    document.body.appendChild(el);
+
+    el.style.visibility = "hidden";
+    // Without visibilityProperty option, visibility:hidden is not checked
+    testing.expectEqual(true, el.checkVisibility());
+    // With visibilityProperty: true, visibility:hidden is detected
+    testing.expectEqual(false, el.checkVisibility({ visibilityProperty: true }));
+
+    el.style.visibility = "collapse";
+    testing.expectEqual(false, el.checkVisibility({ visibilityProperty: true }));
+
+    el.style.visibility = "visible";
+    testing.expectEqual(true, el.checkVisibility({ visibilityProperty: true }));
+
+    el.remove();
+  }
+</script>
+
+<script id="inline_opacity_zero">
+  {
+    const el = document.createElement("div");
+    document.body.appendChild(el);
+
+    el.style.opacity = "0";
+    // Without checkOpacity option, opacity:0 is not checked
+    testing.expectEqual(true, el.checkVisibility());
+    // With checkOpacity: true, opacity:0 is detected
+    testing.expectEqual(false, el.checkVisibility({ checkOpacity: true }));
+
+    el.style.opacity = "0.5";
+    testing.expectEqual(true, el.checkVisibility({ checkOpacity: true }));
+
+    el.style.opacity = "1";
+    testing.expectEqual(true, el.checkVisibility({ checkOpacity: true }));
+
+    el.remove();
+  }
+</script>
+
+<script id="parent_hidden_hides_child">
+  {
+    const parent = document.createElement("div");
+    const child = document.createElement("span");
+    parent.appendChild(child);
+    document.body.appendChild(parent);
+
+    testing.expectEqual(true, child.checkVisibility());
+
+    // display:none on parent hides children (no option needed)
+    parent.style.display = "none";
+    testing.expectEqual(false, child.checkVisibility());
+
+    // visibility:hidden on parent - needs visibilityProperty option
+    parent.style.display = "block";
+    parent.style.visibility = "hidden";
+    testing.expectEqual(true, child.checkVisibility()); // without option
+    testing.expectEqual(false, child.checkVisibility({ visibilityProperty: true }));
+
+    // opacity:0 on parent - needs checkOpacity option
+    parent.style.visibility = "visible";
+    parent.style.opacity = "0";
+    testing.expectEqual(true, child.checkVisibility()); // without option
+    testing.expectEqual(false, child.checkVisibility({ checkOpacity: true }));
+
+    parent.remove();
+  }
+</script>
+
+<style id="style-basic">
+  .hidden-by-class { display: none; }
+  .visible-by-class { display: block; }
+</style>
+<script id="style_tag_basic">
+  {
+    const el = document.createElement("div");
+    document.body.appendChild(el);
+
+    testing.expectEqual(true, el.checkVisibility());
+
+    el.className = "hidden-by-class";
+    testing.expectEqual(false, el.checkVisibility());
+
+    el.className = "visible-by-class";
+    testing.expectEqual(true, el.checkVisibility());
+
+    el.className = "";
+    el.remove();
+  }
+</script>
+
+<style id="style-specificity">
+  .spec-hidden { display: none; }
+  #spec-visible { display: block; }
+</style>
+<script id="specificity_id_beats_class">
+  {
+    const el = document.createElement("div");
+    el.id = "spec-visible";
+    el.className = "spec-hidden";
+    document.body.appendChild(el);
+
+    // ID selector (#spec-visible: display:block) should beat class selector (.spec-hidden: display:none)
+    testing.expectEqual(true, el.checkVisibility());
+
+    el.remove();
+  }
+</script>
+
+<style id="style-order-1">
+  .order-test { display: none; }
+</style>
+<style id="style-order-2">
+  .order-test { display: block; }
+</style>
+<script id="rule_order_later_wins">
+  {
+    const el = document.createElement("div");
+    el.className = "order-test";
+    document.body.appendChild(el);
+
+    // Second style block should win (display: block)
+    testing.expectEqual(true, el.checkVisibility());
+
+    el.remove();
+  }
+</script>
+
+<style id="style-override">
+  .should-be-hidden { display: none; }
+</style>
+<script id="inline_overrides_stylesheet">
+  {
+    const el = document.createElement("div");
+    el.className = "should-be-hidden";
+    document.body.appendChild(el);
+
+    testing.expectEqual(false, el.checkVisibility());
+
+    // Inline style should override
+    el.style.display = "block";
+    testing.expectEqual(true, el.checkVisibility());
+
+    el.remove();
+  }
+</script>
+
+<script id="dynamic_style_element">
+  {
+    const el = document.createElement("div");
+    el.className = "dynamic-style-test";
+    document.body.appendChild(el);
+
+    testing.expectEqual(true, el.checkVisibility());
+
+    // Add a style element
+    const style = document.createElement("style");
+    style.textContent = ".dynamic-style-test { display: none; }";
+    document.head.appendChild(style);
+
+    testing.expectEqual(false, el.checkVisibility());
+
+    // Remove the style element
+    style.remove();
+    testing.expectEqual(true, el.checkVisibility());
+
+    el.remove();
+  }
+</script>
+
+<script id="deep_nesting">
+  {
+    const levels = 5;
+    let current = document.body;
+    const elements = [];
+
+    for (let i = 0; i < levels; i++) {
+      const el = document.createElement("div");
+      current.appendChild(el);
+      elements.push(el);
+      current = el;
+    }
+
+    // All should be visible
+    for (let i = 0; i < levels; i++) {
+      testing.expectEqual(true, elements[i].checkVisibility());
+    }
+
+    // Hide middle element
+    elements[2].style.display = "none";
+
+    // Elements 0, 1 should still be visible
+    testing.expectEqual(true, elements[0].checkVisibility());
+    testing.expectEqual(true, elements[1].checkVisibility());
+
+    // Elements 2, 3, 4 should be hidden
+    testing.expectEqual(false, elements[2].checkVisibility());
+    testing.expectEqual(false, elements[3].checkVisibility());
+    testing.expectEqual(false, elements[4].checkVisibility());
+
+    elements[0].remove();
+  }
+</script>

src/browser/webapi/Document.zig

@@ -586,7 +586,7 @@ pub fn elementFromPoint(self: *Document, x: f64, y: f64, page: *Page) !?*Element
     while (stack.items.len > 0) {
         const node = stack.pop() orelse break;
         if (node.is(Element)) |element| {
-            if (element.checkVisibility(page)) {
+            if (element.checkVisibilityCached(null, page)) {
                 const rect = element.getBoundingClientRectForVisible(page);
                 if (x >= rect.getLeft() and x <= rect.getRight() and y >= rect.getTop() and y <= rect.getBottom()) {
                     topmost = element;

src/browser/webapi/Element.zig

@@ -24,6 +24,7 @@ const String = @import("../../string.zig").String;
 
 const js = @import("../js/js.zig");
 const Page = @import("../Page.zig");
+const StyleManager = @import("../StyleManager.zig");
 const reflect = @import("../reflect.zig");
 
 const Node = @import("Node.zig");
@@ -1041,135 +1042,32 @@ pub fn parentElement(self: *Element) ?*Element {
     return self._proto.parentElement();
 }
 
-const CSSStyleRule = @import("css/CSSStyleRule.zig");
-const StyleSheetList = @import("css/StyleSheetList.zig");
+/// Cache for visibility checks - re-exported from StyleManager for convenience.
+pub const VisibilityCache = StyleManager.VisibilityCache;
 
-pub const CssProperties = struct {
-    display_none: bool = false,
-    visibility_hidden: bool = false,
-    opacity_zero: bool = false,
-    pointer_events_none: bool = false,
+/// Cache for pointer-events checks - re-exported from StyleManager for convenience.
+pub const PointerEventsCache = StyleManager.PointerEventsCache;
+
+pub fn hasPointerEventsNone(self: *Element, cache: ?*PointerEventsCache, page: *Page) bool {
+    return page._style_manager.hasPointerEventsNone(self, cache);
+}
+
+pub fn checkVisibilityCached(self: *Element, cache: ?*VisibilityCache, page: *Page) bool {
+    return !page._style_manager.isHidden(self, cache, .{});
+}
+
+const CheckVisibilityOpts = struct {
+    checkOpacity: bool = false,
+    opacityProperty: bool = false,
+    checkVisibilityCSS: bool = false,
+    visibilityProperty: bool = false,
 };
-
-pub const CssCache = std.AutoHashMapUnmanaged(*Element, CssProperties);
-
-fn getCssProperties(el: *Element, doc_sheets: ?*StyleSheetList, cache: ?*CssCache, page: *Page) CssProperties {
-    if (cache) |c| {
-        if (c.get(el)) |props| return props;
-    }
-
-    var props = CssProperties{};
-
-    // Check stylesheets first
-    if (doc_sheets) |sheets| {
-        for (0..sheets.length()) |i| {
-            const sheet = sheets.item(i) orelse continue;
-            const rules = sheet.getCssRules(page) catch continue;
-            for (0..rules.length()) |j| {
-                const rule = rules.item(j) orelse continue;
-                if (rule.is(CSSStyleRule)) |style_rule| {
-                    const selector = style_rule.getSelectorText();
-                    if (el.matches(selector, page) catch false) {
-                        const style = (style_rule.getStyle(page) catch continue).asCSSStyleDeclaration();
-
-                        const display = style.getPropertyValue("display", page);
-                        if (std.mem.eql(u8, display, "none")) {
-                            props.display_none = true;
-                        } else if (display.len > 0) {
-                            props.display_none = false;
-                        }
-
-                        const visibility = style.getPropertyValue("visibility", page);
-                        if (std.mem.eql(u8, visibility, "hidden") or std.mem.eql(u8, visibility, "collapse")) {
-                            props.visibility_hidden = true;
-                        } else if (visibility.len > 0) {
-                            props.visibility_hidden = false;
-                        }
-
-                        const opacity = style.getPropertyValue("opacity", page);
-                        if (std.mem.eql(u8, opacity, "0")) {
-                            props.opacity_zero = true;
-                        } else if (opacity.len > 0) {
-                            props.opacity_zero = false;
-                        }
-
-                        const pointer_events = style.getPropertyValue("pointer-events", page);
-                        if (std.mem.eql(u8, pointer_events, "none")) {
-                            props.pointer_events_none = true;
-                        } else if (pointer_events.len > 0) {
-                            props.pointer_events_none = false;
-                        }
-                    }
-                }
-            }
-        }
-    }
-
-    // Check inline styles overrides
-    if (el.getOrCreateStyle(page) catch null) |style| {
-        const decl = style.asCSSStyleDeclaration();
-        const display = decl.getPropertyValue("display", page);
-        if (std.mem.eql(u8, display, "none")) {
-            props.display_none = true;
-        } else if (display.len > 0) {
-            props.display_none = false;
-        }
-
-        const visibility = decl.getPropertyValue("visibility", page);
-        if (std.mem.eql(u8, visibility, "hidden") or std.mem.eql(u8, visibility, "collapse")) {
-            props.visibility_hidden = true;
-        } else if (visibility.len > 0) {
-            props.visibility_hidden = false;
-        }
-
-        const opacity = decl.getPropertyValue("opacity", page);
-        if (std.mem.eql(u8, opacity, "0")) {
-            props.opacity_zero = true;
-        } else if (opacity.len > 0) {
-            props.opacity_zero = false;
-        }
-
-        const pointer_events = decl.getPropertyValue("pointer-events", page);
-        if (std.mem.eql(u8, pointer_events, "none")) {
-            props.pointer_events_none = true;
-        } else if (pointer_events.len > 0) {
-            props.pointer_events_none = false;
-        }
-    }
-
-    if (cache) |c| {
-        c.put(page.call_arena, el, props) catch {};
-    }
-
-    return props;
-}
-
-pub fn hasPointerEventsNone(self: *Element, cache: ?*CssCache, page: *Page) bool {
-    const doc_sheets = page.document.getStyleSheets(page) catch null;
-    var current: ?*Element = self;
-    while (current) |el| {
-        const props = el.getCssProperties(doc_sheets, cache, page);
-        if (props.pointer_events_none) return true;
-        current = el.parentElement();
-    }
-    return false;
-}
-
-pub fn checkVisibilityCached(self: *Element, cache: ?*CssCache, page: *Page) bool {
-    const doc_sheets = page.document.getStyleSheets(page) catch null;
-    var current: ?*Element = self;
-
-    while (current) |el| {
-        const props = getCssProperties(el, doc_sheets, cache, page);
-        if (props.display_none or props.visibility_hidden or props.opacity_zero) return false;
-        current = el.parentElement();
-    }
-
-    return true;
-}
-
-pub fn checkVisibility(self: *Element, page: *Page) bool {
-    return self.checkVisibilityCached(null, page);
+pub fn checkVisibility(self: *Element, opts_: ?CheckVisibilityOpts, page: *Page) bool {
+    const opts = opts_ orelse CheckVisibilityOpts{};
+    return !page._style_manager.isHidden(self, null, .{
+        .check_opacity = opts.checkOpacity or opts.opacityProperty,
+        .check_visibility = opts.visibilityProperty or opts.checkVisibilityCSS,
+    });
 }
 
 fn getElementDimensions(self: *Element, page: *Page) struct { width: f64, height: f64 } {
@@ -1206,7 +1104,7 @@ fn getElementDimensions(self: *Element, page: *Page) struct { width: f64, height
 }
 
 pub fn getClientWidth(self: *Element, page: *Page) f64 {
-    if (!self.checkVisibility(page)) {
+    if (!self.checkVisibilityCached(null, page)) {
         return 0.0;
     }
     const dims = self.getElementDimensions(page);
@@ -1214,7 +1112,7 @@ pub fn getClientWidth(self: *Element, page: *Page) f64 {
 }
 
 pub fn getClientHeight(self: *Element, page: *Page) f64 {
-    if (!self.checkVisibility(page)) {
+    if (!self.checkVisibilityCached(null, page)) {
         return 0.0;
     }
     const dims = self.getElementDimensions(page);
@@ -1222,7 +1120,7 @@ pub fn getClientHeight(self: *Element, page: *Page) f64 {
 }
 
 pub fn getBoundingClientRect(self: *Element, page: *Page) DOMRect {
-    if (!self.checkVisibility(page)) {
+    if (!self.checkVisibilityCached(null, page)) {
         return .{
             ._x = 0.0,
             ._y = 0.0,
@@ -1252,7 +1150,7 @@ pub fn getBoundingClientRectForVisible(self: *Element, page: *Page) DOMRect {
 }
 
 pub fn getClientRects(self: *Element, page: *Page) ![]DOMRect {
-    if (!self.checkVisibility(page)) {
+    if (!self.checkVisibilityCached(null, page)) {
         return &.{};
     }
     const rects = try page.call_arena.alloc(DOMRect, 1);
@@ -1297,7 +1195,7 @@ pub fn getScrollWidth(self: *Element, page: *Page) f64 {
 }
 
 pub fn getOffsetHeight(self: *Element, page: *Page) f64 {
-    if (!self.checkVisibility(page)) {
+    if (!self.checkVisibilityCached(null, page)) {
         return 0.0;
     }
     const dims = self.getElementDimensions(page);
@@ -1305,7 +1203,7 @@ pub fn getOffsetHeight(self: *Element, page: *Page) f64 {
 }
 
 pub fn getOffsetWidth(self: *Element, page: *Page) f64 {
-    if (!self.checkVisibility(page)) {
+    if (!self.checkVisibilityCached(null, page)) {
         return 0.0;
     }
     const dims = self.getElementDimensions(page);
@@ -1313,14 +1211,14 @@ pub fn getOffsetWidth(self: *Element, page: *Page) f64 {
 }
 
 pub fn getOffsetTop(self: *Element, page: *Page) f64 {
-    if (!self.checkVisibility(page)) {
+    if (!self.checkVisibilityCached(null, page)) {
         return 0.0;
     }
     return calculateDocumentPosition(self.asNode());
 }
 
 pub fn getOffsetLeft(self: *Element, page: *Page) f64 {
-    if (!self.checkVisibility(page)) {
+    if (!self.checkVisibilityCached(null, page)) {
         return 0.0;
     }
     return calculateSiblingPosition(self.asNode());

src/browser/webapi/css/CSSStyleDeclaration.zig

@@ -77,10 +77,11 @@ pub fn item(self: *const CSSStyleDeclaration, index: u32) []const u8 {
 
 pub fn getPropertyValue(self: *const CSSStyleDeclaration, property_name: []const u8, page: *Page) []const u8 {
     const normalized = normalizePropertyName(property_name, &page.buf);
-    const prop = self.findProperty(normalized) orelse {
+    const wrapped = String.wrap(normalized);
+    const prop = self.findProperty(wrapped) orelse {
         // Only return default values for computed styles
         if (self._is_computed) {
-            return getDefaultPropertyValue(self, normalized);
+            return getDefaultPropertyValue(self, wrapped);
         }
         return "";
     };
@@ -89,7 +90,7 @@ pub fn getPropertyValue(self: *const CSSStyleDeclaration, property_name: []const
 
 pub fn getPropertyPriority(self: *const CSSStyleDeclaration, property_name: []const u8, page: *Page) []const u8 {
     const normalized = normalizePropertyName(property_name, &page.buf);
-    const prop = self.findProperty(normalized) orelse return "";
+    const prop = self.findProperty(.wrap(normalized)) orelse return "";
     return if (prop._important) "important" else "";
 }
 
@@ -120,7 +121,7 @@ fn setPropertyImpl(self: *CSSStyleDeclaration, property_name: []const u8, value:
     const normalized_value = try normalizePropertyValue(page.call_arena, normalized, value);
 
     // Find existing property
-    if (self.findProperty(normalized)) |existing| {
+    if (self.findProperty(.wrap(normalized))) |existing| {
         existing._value = try String.init(page.arena, normalized_value, .{});
         existing._important = important;
         return;
@@ -144,7 +145,7 @@ pub fn removeProperty(self: *CSSStyleDeclaration, property_name: []const u8, pag
 
 fn removePropertyImpl(self: *CSSStyleDeclaration, property_name: []const u8, page: *Page) ![]const u8 {
     const normalized = normalizePropertyName(property_name, &page.buf);
-    const prop = self.findProperty(normalized) orelse return "";
+    const prop = self.findProperty(.wrap(normalized)) orelse return "";
 
     // the value might not be on the heap (it could be inlined in the small string
     // optimization), so we need to dupe it.
@@ -208,11 +209,11 @@ pub fn format(self: *const CSSStyleDeclaration, writer: *std.Io.Writer) !void {
     }
 }
 
-fn findProperty(self: *const CSSStyleDeclaration, name: []const u8) ?*Property {
+pub fn findProperty(self: *const CSSStyleDeclaration, name: String) ?*Property {
     var node = self._properties.first;
     while (node) |n| {
         const prop = Property.fromNodeLink(n);
-        if (prop._name.eqlSlice(name)) {
+        if (prop._name.eql(name)) {
             return prop;
         }
         node = n.next;
@@ -617,26 +618,36 @@ fn isLengthProperty(name: []const u8) bool {
     return length_properties.has(name);
 }
 
-fn getDefaultPropertyValue(self: *const CSSStyleDeclaration, normalized_name: []const u8) []const u8 {
-    if (std.mem.eql(u8, normalized_name, "visibility")) {
-        return "visible";
+fn getDefaultPropertyValue(self: *const CSSStyleDeclaration, name: String) []const u8 {
+    switch (name.len) {
+        5 => {
+            if (name.eql(comptime .wrap("color"))) {
+                const element = self._element orelse return "";
+                return getDefaultColor(element);
+            }
+        },
+        7 => {
+            if (name.eql(comptime .wrap("opacity"))) {
+                return "1";
+            }
+            if (name.eql(comptime .wrap("display"))) {
+                const element = self._element orelse return "";
+                return getDefaultDisplay(element);
+            }
+        },
+        10 => {
+            if (name.eql(comptime .wrap("visibility"))) {
+                return "visible";
+            }
+        },
+        16 => {
+            if (name.eqlSlice("background-color")) {
+                // transparent
+                return "rgba(0, 0, 0, 0)";
+            }
+        },
+        else => {},
     }
-    if (std.mem.eql(u8, normalized_name, "opacity")) {
-        return "1";
-    }
-    if (std.mem.eql(u8, normalized_name, "display")) {
-        const element = self._element orelse return "";
-        return getDefaultDisplay(element);
-    }
-    if (std.mem.eql(u8, normalized_name, "color")) {
-        const element = self._element orelse return "";
-        return getDefaultColor(element);
-    }
-    if (std.mem.eql(u8, normalized_name, "background-color")) {
-        // transparent
-        return "rgba(0, 0, 0, 0)";
-    }
-
     return "";
 }
 

src/browser/webapi/css/CSSStyleSheet.zig

@@ -69,12 +69,19 @@ pub fn insertRule(self: *CSSStyleSheet, rule: []const u8, maybe_index: ?u32, pag
 
     const rules = try self.getCssRules(page);
     try rules.insert(index, style_rule._proto, page);
+
+    // Notify StyleManager that rules have changed
+    page._style_manager.sheetModified();
+
     return index;
 }
 
 pub fn deleteRule(self: *CSSStyleSheet, index: u32, page: *Page) !void {
     const rules = try self.getCssRules(page);
     try rules.remove(index);
+
+    // Notify StyleManager that rules have changed
+    page._style_manager.sheetModified();
 }
 
 pub fn replace(self: *CSSStyleSheet, text: []const u8, page: *Page) !js.Promise {
@@ -99,6 +106,9 @@ pub fn replaceSync(self: *CSSStyleSheet, text: []const u8, page: *Page) !void {
         try rules.insert(index, style_rule._proto, page);
         index += 1;
     }
+
+    // Notify StyleManager that rules have changed
+    page._style_manager.sheetModified();
 }
 
 pub const JsApi = struct {

src/browser/webapi/css/StyleSheetList.zig

@@ -24,6 +24,15 @@ pub fn add(self: *StyleSheetList, sheet: *CSSStyleSheet, page: *Page) !void {
     try self._sheets.append(page.arena, sheet);
 }
 
+pub fn remove(self: *StyleSheetList, sheet: *CSSStyleSheet) void {
+    for (self._sheets.items, 0..) |s, i| {
+        if (s == sheet) {
+            _ = self._sheets.orderedRemove(i);
+            return;
+        }
+    }
+}
+
 pub const JsApi = struct {
     pub const bridge = js.Bridge(StyleSheetList);
 

src/browser/webapi/element/html/Style.zig

@@ -106,7 +106,10 @@ pub fn getSheet(self: *Style, page: *Page) !?*CSSStyleSheet {
 
 pub fn styleAddedCallback(self: *Style, page: *Page) !void {
     // Force stylesheet initialization so rules are parsed immediately
-    _ = self.getSheet(page) catch null;
+    if (self.getSheet(page) catch null) |sheet| {
+        // Notify StyleManager about the new stylesheet
+        page._style_manager.sheetAdded(sheet) catch {};
+    }
 
     // if we're planning on navigating to another page, don't trigger load event.
     if (page.isGoingAway()) {