Make the body not scrollable and make a scrollable container div to host #extension-settings.

chrome/browser/resources/extensions/extensions.css

Index: chrome/browser/resources/extensions/extensions.css
diff --git a/chrome/browser/resources/extensions/extensions.css b/chrome/browser/resources/extensions/extensions.css
index 579fdaa8e41b2e7bdd4bae809a300d1822da2327..276ae2c631149c96808fa9b9bc7904930e8ced74 100644
--- a/chrome/browser/resources/extensions/extensions.css
+++ b/chrome/browser/resources/extensions/extensions.css
@@ -2,6 +2,12 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file. */
 
+html,
+body {
+  height: 100%;
+  overflow: hidden;
+}
+
 html.loading * {
   -webkit-transition-duration: 0 !important;
 }
@@ -90,6 +96,11 @@ html:not(.focus-outline-visible)
 
 /* Contents */
 
+#page-container {
+  height: 100%;
+  overflow-y: auto;
+}
+
 #extension-settings {
   max-width: 738px;
 }