diff --git a/composer.json b/composer.json
index a71c617dfcd..7f692e4a526 100644
--- a/composer.json
+++ b/composer.json
@@ -17,7 +17,7 @@
     "ampproject/amp-toolbox": "0.11.6",
     "cweagans/composer-patches": "^1.0",
     "fasterimage/fasterimage": "1.5.0",
-    "sabberworm/php-css-parser": "8.5.1"
+    "sabberworm/php-css-parser": "9.0.0"
   },
   "require-dev": {
     "automattic/vipwpcs": "^3.0",
diff --git a/composer.lock b/composer.lock
index bc0547295ec..55b32a0cab2 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "4ec9f08e4507102e813b4a2d385c2097",
+    "content-hash": "a3f57fd20071b8895d95ebdd76f8d8d7",
     "packages": [
         {
             "name": "ampproject/amp-toolbox",
@@ -189,24 +189,32 @@
         },
         {
             "name": "sabberworm/php-css-parser",
-            "version": "v8.5.1",
+            "version": "v9.0.0",
             "source": {
                 "type": "git",
                 "url": "https://github.com/MyIntervals/PHP-CSS-Parser.git",
-                "reference": "4a3d572b0f8b28bb6fd016ae8bbfc445facef152"
+                "reference": "54574e3de2f8cdc91175ffd2337e5c6804a7d729"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/MyIntervals/PHP-CSS-Parser/zipball/4a3d572b0f8b28bb6fd016ae8bbfc445facef152",
-                "reference": "4a3d572b0f8b28bb6fd016ae8bbfc445facef152",
+                "url": "https://api.github.com/repos/MyIntervals/PHP-CSS-Parser/zipball/54574e3de2f8cdc91175ffd2337e5c6804a7d729",
+                "reference": "54574e3de2f8cdc91175ffd2337e5c6804a7d729",
                 "shasum": ""
             },
             "require": {
                 "ext-iconv": "*",
-                "php": ">=5.6.20"
+                "php": "^7.2.0 || ~8.0.0 || ~8.1.0 || ~8.2.0 || ~8.3.0 || ~8.4.0"
             },
             "require-dev": {
-                "phpunit/phpunit": "^5.7.27"
+                "php-parallel-lint/php-parallel-lint": "1.4.0",
+                "phpstan/extension-installer": "1.4.3",
+                "phpstan/phpstan": "1.12.28 || 2.1.19",
+                "phpstan/phpstan-phpunit": "1.4.2 || 2.0.7",
+                "phpstan/phpstan-strict-rules": "1.6.2 || 2.0.6",
+                "phpunit/phpunit": "8.5.42",
+                "rawr/phpunit-data-provider": "3.3.1",
+                "rector/rector": "1.2.10 || 2.1.2",
+                "rector/type-perfect": "1.0.0 || 2.1.0"
             },
             "suggest": {
                 "ext-mbstring": "for parsing UTF-8 CSS"
@@ -214,7 +222,7 @@
             "type": "library",
             "extra": {
                 "branch-alias": {
-                    "dev-main": "9.0.x-dev"
+                    "dev-main": "9.1.x-dev"
                 }
             },
             "autoload": {
@@ -248,9 +256,9 @@
             ],
             "support": {
                 "issues": "https://github.com/MyIntervals/PHP-CSS-Parser/issues",
-                "source": "https://github.com/MyIntervals/PHP-CSS-Parser/tree/v8.5.1"
+                "source": "https://github.com/MyIntervals/PHP-CSS-Parser/tree/v9.0.0"
             },
-            "time": "2024-02-15T16:41:13+00:00"
+            "time": "2025-07-27T07:24:01+00:00"
         },
         {
             "name": "willwashburn/stream",