[DevTools] Add groups to device select.

Source/devtools/front_end/overrides.css

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 286 matching lines @@
 .overrides-view .overrides-footer::before {
     background-image: url(Images/statusbarButtonGlyphs_2x.png);
 }
 } /* media */
 
 .overrides-view .overrides-footer .warning-icon-small {
     margin-right: 3px;
 }
 
 .overrides-splash-screen {
-    display: flex;
-    align-items: center;
+    display: block;
     padding: 3px 10px;
 }
 
+.overrides-splash-screen > button {
+    margin: -4px 0;
+}
+
 .overrides-reset-button {
     margin: 9px 0 0 17px;
 }