[MD settings] change color values to --paper-variable colors

chrome/browser/resources/settings/settings_shared.css

 /* Copyright 2015 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. */
 
 /**
  * @fileoverview
  * Common styles for Material Design settings.
  */
 
 h2 {
-  color: #9e9e9e;
+  color: var(--paper-grey-500);
   font-size: 100%;
   font-weight: normal;
   margin-bottom: 20px;
   margin-top: 30px;
 }
 
 iron-icon {
   color: #969696;
 }
 
@@ skipping 70 matching lines @@
   padding-top: 6px;
   text-transform: none;
 }
 
 .settings-card {
   padding: 8px 0;
 }
 
 .settings-box {
   @apply(--layout-center);
-  border-top: 1px solid #e0e0e0;
+  border-top: 1px solid var(--paper-grey-300);
   display: flex;
   min-height: 40px;
   padding: 0 20px;
 }
 
 .settings-box.first {
   border-top: none;
 }
 
 .settings-box.block {
@@ skipping 15 matching lines @@
 .settings-box paper-item iron-icon {
   /* Same padding as paper-icon-button. */
   padding: 8px;
 }
 
 .vertical-list > div:first-of-type {
   border-top: none;
 }
 
 .vertical-list > div {
-  border-top: 1px solid #e0e0e0;
+  border-top: 1px solid var(--paper-grey-300);
 }