diff --git a/gulpfile.js b/gulpfile.js
index ffc508355..5d98642b6 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -190,6 +190,8 @@ function createWebpackConfig(
     DEFAULT_PREFERENCES: defaultPreferencesDir
       ? getDefaultPreferences(defaultPreferencesDir)
       : {},
+    DIALOG_POLYFILL_CSS:
+      defines.GENERIC && !defines.SKIP_BABEL ? getDialogPolyfillCSS() : "",
   });
   const licenseHeaderLibre = fs
     .readFileSync("./src/license_header_libre.js")
@@ -736,6 +738,12 @@ function getDefaultPreferences(dir) {
   return AppOptions.getAll(OptionKind.PREFERENCE);
 }
 
+function getDialogPolyfillCSS() {
+  return fs
+    .readFileSync("node_modules/dialog-polyfill/dist/dialog-polyfill.css")
+    .toString();
+}
+
 gulp.task("locale", function () {
   const VIEWER_LOCALE_OUTPUT = "web/locale/";
 
@@ -1519,6 +1527,8 @@ function buildLib(defines, dir) {
     DEFAULT_PREFERENCES: getDefaultPreferences(
       defines.SKIP_BABEL ? "lib/" : "lib-legacy/"
     ),
+    DIALOG_POLYFILL_CSS:
+      defines.GENERIC && !defines.SKIP_BABEL ? getDialogPolyfillCSS() : "",
   });
 
   const inputStream = merge([
diff --git a/web/overlay_manager.js b/web/overlay_manager.js
index e4d7378e1..cebc1953a 100644
--- a/web/overlay_manager.js
+++ b/web/overlay_manager.js
@@ -44,6 +44,15 @@ class OverlayManager {
     ) {
       const dialogPolyfill = require("dialog-polyfill/dist/dialog-polyfill.js");
       dialogPolyfill.registerDialog(dialog);
+
+      if (!this._dialogPolyfillCSS) {
+        this._dialogPolyfillCSS = true;
+
+        const style = document.createElement("style");
+        style.textContent = PDFJSDev.eval("DIALOG_POLYFILL_CSS");
+
+        document.head.insertBefore(style, document.head.firstElementChild);
+      }
     }
 
     dialog.addEventListener("cancel", evt => {