Remove unused assets, update old assets

chrome/browser/resources/options/import_data_overlay.css

 /* Copyright (c) 2012 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. */
 
 #import-data-overlay {
   width: 400px;
 }
 
 #import-from-div {
   margin-bottom: 20px;
 }
 
 #import-checkboxes > div:not(:first-child) {
   -webkit-padding-start: 8px;
 }
 
 #import-throbber {
   margin: 4px 10px;
   vertical-align: middle;
   visibility: hidden;
 }
 
 #import-success-header {
   font-size: 1.2em;
 }
 
 #import-success-image {
-  margin: 20px;
-  text-align: center;
+  -webkit-mask-image: url(../../../../ui/webui/resources/images/check_circle.svg);
+  -webkit-mask-position: center;
+  -webkit-mask-repeat: no-repeat;
+  -webkit-mask-size: 96px;
+  background-color: rgb(15, 157, 88);
+  height: 96px;
+  margin: 20px 0;
+  width: 100%;
 }