From 466cdb4ee70d134bf740cf71b0448be94edc15ad Mon Sep 17 00:00:00 2001
From: Karl Seguin <k@openmymind.io>
Date: Sat, 31 Jan 2026 10:44:56 +0800
Subject: [PATCH] improve correctness of CSS.escape

---
 src/browser/tests/css.html |  6 ++++--
 src/browser/webapi/CSS.zig | 26 ++++++++++++++++++--------
 2 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/src/browser/tests/css.html b/src/browser/tests/css.html
index ac0b6aba..ee0db0e0 100644
--- a/src/browser/tests/css.html
+++ b/src/browser/tests/css.html
@@ -20,8 +20,10 @@
   {
     testing.expectEqual('\\30 abc', CSS.escape('0abc'));
     testing.expectEqual('\\31 23', CSS.escape('123'));
-    testing.expectEqual('\\-test', CSS.escape('-test'));
-    testing.expectEqual('\\--test', CSS.escape('--test'));
+    testing.expectEqual('\\-', CSS.escape('-'));
+    testing.expectEqual('-test', CSS.escape('-test'));
+    testing.expectEqual('--test', CSS.escape('--test'));
+    testing.expectEqual('-\\33 ', CSS.escape('-3'));
   }
 </script>
 
diff --git a/src/browser/webapi/CSS.zig b/src/browser/webapi/CSS.zig
index a2f320f7..2eed5cf3 100644
--- a/src/browser/webapi/CSS.zig
+++ b/src/browser/webapi/CSS.zig
@@ -42,15 +42,23 @@ pub fn parseDimension(value: []const u8) ?f64 {
 /// https://drafts.csswg.org/cssom/#the-css.escape()-method
 pub fn escape(_: *const CSS, value: []const u8, page: *Page) ![]const u8 {
     if (value.len == 0) {
-        return error.InvalidCharacterError;
+        return "";
     }
 
     const first = value[0];
+    if (first == '-' and value.len == 1) {
+        return "\\-";
+    }
 
     // Count how many characters we need for the output
     var out_len: usize = escapeLen(true, first);
-    for (value[1..]) |c| {
-        out_len += escapeLen(false, c);
+    for (value[1..], 0..) |c, i| {
+        // Second char (i==0) is a digit and first is '-', needs hex escape
+        if (i == 0 and first == '-' and c >= '0' and c <= '9') {
+            out_len += 2 + hexDigitsNeeded(c);
+        } else {
+            out_len += escapeLen(false, c);
+        }
     }
 
     if (out_len == value.len) {
@@ -67,8 +75,13 @@ pub fn escape(_: *const CSS, value: []const u8, page: *Page) ![]const u8 {
         pos = 1;
     }
 
-    for (value[1..]) |c| {
-        if (!needsEscape(false, c)) {
+    for (value[1..], 0..) |c, i| {
+        // Second char (i==0) is a digit and first is '-', needs hex escape
+        if (i == 0 and first == '-' and c >= '0' and c <= '9') {
+            result[pos] = '\\';
+            const hex_str = std.fmt.bufPrint(result[pos + 1 ..], "{x} ", .{c}) catch unreachable;
+            pos += 1 + hex_str.len;
+        } else if (!needsEscape(false, c)) {
             result[pos] = c;
             pos += 1;
         } else {
@@ -105,9 +118,6 @@ fn needsEscape(comptime is_first: bool, c: u8) bool {
         if (c >= '0' and c <= '9') {
             return true;
         }
-        if (c == '-') {
-            return true;
-        }
     }
 
     // Characters that need escaping