Stop showing orange highlight when thumbnail window is active.

ui/file_manager/gallery/css/gallery.css

 /* Copyright (c) 2014 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 {
   -webkit-user-select: none;
   background-color: black;
   font-size: 84%;
   margin: 0;
 }
@@ skipping 1253 matching lines @@
 .debug-me .load-target-file-entry::before {
   background-color: rgba(0, 0, 255, 0.3);
 }
 
 /**
  * Thumbnail view.
  */
 .thumbnail-view {
   display: block;
   height: 100%;
+  outline: none;
   overflow-y: scroll;
 }
 
 .thumbnail-view ul {
   -webkit-padding-end: 4px;
   -webkit-padding-start: 0;
   margin: 0;
   padding-top: 52px; /* Toolbar height (48px) + Margin (4px) */
   padding-bottom: 0;
 }
@@ skipping 79 matching lines @@
 .thumbnail-view .animation-thumbnail {
   background-repeat: no-repeat;
   background-size: cover;
   display: none;
   position: absolute;
 }
 
 .thumbnail-view .animation-thumbnail.animating {
   display: block;
 }