Update WebUI calls to use extensions namespace, update IDs in c/b/r/extensions

chrome/browser/resources/extensions/extensions.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. */
 
 html,
 body {
   height: 100%;
   overflow: hidden;
 }
 
@@ skipping 266 matching lines @@
 /* Overlays */
 
 #overlay {
   z-index: 5;
 }
 
 #overlay .page:not(.showing) {
   display: none;
 }
 
-#dropTargetOverlay {
+#drop-target-overlay {
   color: rgb(48, 57, 66);
   font-size: 18px;
   text-align: center;
 }
 
-#dropTargetOverlay div {
+#drop-target-overlay div {
   margin: 1em;
 }
 
 .location-text {
   display: block;
   width: 100px;
 }
 
 /* Trash */
 
@@ skipping 46 matching lines @@
 /* Sideload Wipeout */
 
 .sideload-wipeout-learn-more {
   text-decoration: none;
 }
 
 .sideload-wipeout-banner .page-banner-text {
   -webkit-padding-start: 8px;
   background-image: none;
 }