Change color of ripple effects and tab focus of toolbar buttons in Files

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 602 matching lines @@
 
 .gallery > .toolbar button {
   background-color: transparent;
   border: 0;
   padding: 0;
   position: relative;
 }
 
 .gallery > .toolbar paper-button:focus,
 .gallery > .toolbar button:focus {
-  background-color: rgba(0, 0, 0, 0.3);
+  background-color: rgba(255, 255, 255, 0.2);
 }
 
 .gallery > .toolbar button:focus {
   outline: none;
 }
 
 .gallery > .toolbar button.using-mouse:focus {
   background-color: transparent;
 }
 
@@ skipping 789 matching lines @@
 .thumbnail-view .animation-thumbnail {
   background-repeat: no-repeat;
   background-size: cover;
   display: none;
   position: absolute;
 }
 
 .thumbnail-view .animation-thumbnail.animating {
   display: block;
 }