[FileBrowser] Fixed default hover state.

chrome/browser/resources/file_manager/css/file_manager.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 {
   height: 100%;
 }
 
 html.col-resize * {
   cursor: col-resize !important;
@@ skipping 500 matching lines @@
     url('../images/files/ui/search_clear_hover.png') 1x,
     url('../images/files/ui/2x/search_clear_hover.png') 2x);
 }
 
 #search-box::-webkit-search-cancel-button:active {
   background-image: -webkit-image-set(
     url('../images/files/ui/search_clear_pressed.png') 1x,
     url('../images/files/ui/2x/search_clear_pressed.png') 2x);
 }
 
-button#detail-view {
+button#detail-view:before {
   background-image: -webkit-image-set(
     url('../images/files/ui/view_list_black.png') 1x,
     url('../images/files/ui/2x/view_list_black.png') 2x);
-  background-position: center;
-  background-repeat: no-repeat;
 }
 
-
-button#thumbnail-view {
+button#thumbnail-view:before {
   background-image: -webkit-image-set(
     url('../images/files/ui/view_thumbs_black.png') 1x,
     url('../images/files/ui/2x/view_thumbs_black.png') 2x);
+}
+
+button#detail-view:before,
+button#thumbnail-view:before {
   background-position: center;
   background-repeat: no-repeat;
+  bottom: 0;
+  content: '';
+  left: 0;
+  opacity: 0.5;
+  position: absolute;
+  right: 0;
+  top: 0;
 }
 
+button#detail-view[disabled]:before,
+button#thumbnail-view[disabled]:before {
+  opacity: 0.75;
+}
+
+button#detail-view:hover:before,
+button#thumbnail-view:hover:before {
+  opacity: 1;
+}
+
+
 /* When detail-view is not disabled (thus thumbnail view is disabled), push
    it up a little, to make it's right glowing border visible while focused.*/
 button#detail-view:not([disabled]) {
   z-index: 2;
 }
 
 .filelist-panel {
   -webkit-box-flex: 1;
   -webkit-box-orient: vertical;
   display: -webkit-box;
@@ skipping 831 matching lines @@
 body[type='open-file'] [visibleif]:not([visibleif~='open-file']),
 body[type='open-multi-file'] [visibleif]:not([visibleif~='open-multi-file']),
 body[type='full-page'] [visibleif]:not([visibleif~='full-page']) {
   display: none;
 }
 
 body:not([ctrl-pressing]) [visibleif='ctrl'] {
   display: none;
 }
 
-#gdata-settings {
+#gdata-settings:before {
   background-image: url('../images/files/ui/settings.svg');
   background-position: 20px center;
   background-repeat: no-repeat;
+  bottom: 0;
+  content: '';
+  left: 0;
+  opacity: 0.75;
+  position: absolute;
+  right: 0;
+  top: 0;
+}
+
+#gdata-settings:hover:before {
+  opacity: 1;
+}
+
+
+#gdata-settings {
   overflow: hidden;
   text-align: left;
   width: 54px;
 }
 
 #gdata-settings span.disclosureindicator {
   float: none;
   margin-left: 42px;
 }
 
@@ skipping 150 matching lines @@
 }
 
 #new-folder {
   margin-right: 30px;
 }
 
 #default-action-dialog {
   min-width: 300px;
   width: auto;
 }