diff --git a/package.json b/package.json
index d14755ec823..4bdf03697c3 100644
--- a/package.json
+++ b/package.json
@@ -54,5 +54,8 @@
     "ts_library-test": "./third_party/typescript/tests/verify_ts_libary.sh",
     "unittest": "scripts/test/run_unittests.py --no-text-coverage",
     "watch": "third_party/node/node.py --output scripts/watch_build.js"
+  },
+  "devDependencies": {
+    "sync-fetch": "latest"
   }
 }
diff --git a/scripts/build/generate_css_js_files.js b/scripts/build/generate_css_js_files.js
index bd1770528de..0a81027f743 100644
--- a/scripts/build/generate_css_js_files.js
+++ b/scripts/build/generate_css_js_files.js
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 const fs = require('fs');
 const path = require('path');
+const fetch = require('sync-fetch');
 const CleanCSS = require('clean-css');
 const [, , isDebugString, targetName, srcDir, targetGenDir, files] = process.argv;
 
@@ -11,6 +12,8 @@ const configFiles = [];
 const cleanCSS = new CleanCSS();
 const isDebug = isDebugString === 'true';
 
+const constructibleStyleSheetsPolyfill = fetch('https://unpkg.com/construct-style-sheets-polyfill@3.0.0/dist/adoptedStyleSheets.js').text();
+
 for (const fileName of filenames) {
   let output = fs.readFileSync(path.join(srcDir, fileName), {encoding: 'utf8', flag: 'r'});
   output = output.replace(/\`/g, '\\\'');
@@ -18,9 +21,12 @@ for (const fileName of filenames) {
 
   fs.writeFileSync(
       path.join(targetGenDir, fileName + '.js'),
-      `// Copyright ${new Date().getFullYear()} The Chromium Authors. All rights reserved.
+      `${constructibleStyleSheetsPolyfill}
+ 
+// Copyright ${new Date().getFullYear()} The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
+
 const styles = new CSSStyleSheet();
 styles.replaceSync(
 \`${isDebug ? output : cleanCSS.minify(output).styles}