[FRE] Show scroll bar if window is too small.

chrome/browser/resources/welcome/welcome.css

 /* Copyright 2016 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. */
 
 body {
   align-items: center;
   color: var(--paper-grey-900);
   display: flex;
   flex-direction: column;
   font-size: 100%;
   justify-content: center;
+  margin: 0;
   min-height: 100vh;
-  overflow-y: hidden;
 }
 
 @keyframes slideUpContent {
   from {
     transform: translateY(186px);
   }
 }
 
 @keyframes fadeIn {
   from {
@@ skipping 68 matching lines @@
   }
   70.27% {
     transform: matrix3d(0.999, 0, 0, 0, 0, 0.999, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1);
   }
   100% {
     transform: matrix3d(1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1);
   }
 }
 
 .content {
+  height: 100%;
+  overflow-y: hidden;
+}
+
+.slider {
   align-items: center;
   animation: slideUpContent 600ms 1.8s cubic-bezier(.4, .2, 0, 1) both;
   display: flex;
   flex: 1;
   flex-direction: column;
   justify-content: center;
   max-width: 500px;
 }
 
 .heading {
@@ skipping 98 matching lines @@
   height: 24px;
   position: absolute;
   width: 74px;
 }
 
 @media(max-height: 608px) {
   .watermark {
     display: none;
   }
 }