Don't treat \ as an escape inside CSS comments

Per the CSS Syntax spec, a comment ends at the first `*/`; escapes are
not processed inside comments. The parser skipped the character after a
`\`, so a comment like `/* C:\temp\*/` was never closed and swallowed
(or corrupted) the CSS that followed it.

CHANGELOG.md

@@ -33,6 +33,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Only normalize top-level `and`, `or`, and `not` keywords in `supports-[…]` variants (e.g. `selector(a: not (.foo))` → `selector(a:not(.foo))`) ([#20420](https://github.com/tailwindlabs/tailwindcss/pull/20420))
 - Don't warn about Angular's `::ng-deep` and `:host-context()` when optimizing CSS ([#20434](https://github.com/tailwindlabs/tailwindcss/pull/20434))
 - Don't generate CSS for candidates containing an empty additional modifier (e.g. `bg-red-500/50/` and `group-hover/foo//bar:flex`) ([#20466](https://github.com/tailwindlabs/tailwindcss/pull/20466))
+- Ensure CSS comments ending with `\*/` are closed correctly instead of swallowing the CSS that follows (e.g. `/* C:\temp\*/`)
 
 ## [4.3.3] - 2026-07-16
 

packages/tailwindcss/src/css-parser.test.ts

@@ -31,6 +31,23 @@ describe.each(['Unix', 'Windows'])('Line endings: %s', (lineEndings) => {
       ).toEqual([])
     })
 
+    it('should end a comment at `*/` even when it is preceded by a `\\`', () => {
+      expect(
+        parse(css`
+          /* C:\temp\*/
+          .foo {
+            color: red;
+          }
+        `),
+      ).toEqual([
+        {
+          kind: 'rule',
+          selector: '.foo',
+          nodes: [{ kind: 'declaration', property: 'color', value: 'red', important: false }],
+        },
+      ])
+    })
+
     it('should parse a comment inside of a selector and ignore it', () => {
       expect(
         parse(css`
@@ -448,6 +465,28 @@ describe.each(['Unix', 'Windows'])('Line endings: %s', (lineEndings) => {
         ])
       })
 
+      it('should end a comment in a custom property at `*/` even when it is preceded by a `\\`', () => {
+        expect(
+          parse(css`
+            --foo: /* C:\temp\*/ bar;
+            --bar: /* baz */ qux;
+          `),
+        ).toEqual([
+          {
+            kind: 'declaration',
+            property: '--foo',
+            value: '/* C:\\temp\\*/ bar',
+            important: false,
+          },
+          {
+            kind: 'declaration',
+            property: '--bar',
+            value: '/* baz */ qux',
+            important: false,
+          },
+        ])
+      })
+
       it('should parse empty custom properties', () => {
         expect(
           parse(css`

packages/tailwindcss/src/css-parser.ts

@@ -134,13 +134,9 @@ export function parse(input: string, opts?: ParseOptions) {
       for (let j = i + 2; j < input.length; j++) {
         peekChar = input.charCodeAt(j)
 
-        // Current character is a `\` therefore the next character is escaped.
-        if (peekChar === BACKSLASH) {
-          j += 1
-        }
-
-        // End of the comment
-        else if (peekChar === ASTERISK && input.charCodeAt(j + 1) === SLASH) {
+        // End of the comment. Escapes are not processed inside of comments,
+        // so a `\` right before the closing `*/` does not escape it.
+        if (peekChar === ASTERISK && input.charCodeAt(j + 1) === SLASH) {
           i = j + 1
           break
         }
@@ -224,13 +220,9 @@ export function parse(input: string, opts?: ParseOptions) {
         else if (peekChar === SLASH && input.charCodeAt(j + 1) === ASTERISK) {
           for (let k = j + 2; k < input.length; k++) {
             peekChar = input.charCodeAt(k)
-            // Current character is a `\` therefore the next character is escaped.
-            if (peekChar === BACKSLASH) {
-              k += 1
-            }
 
-            // End of the comment
-            else if (peekChar === ASTERISK && input.charCodeAt(k + 1) === SLASH) {
+            // End of the comment. Escapes are not processed inside of comments.
+            if (peekChar === ASTERISK && input.charCodeAt(k + 1) === SLASH) {
               j = k + 1
               break
             }