DevTools: [Icons] normalize icon sizes

third_party/WebKit/Source/devtools/front_end/elements/stylesSectionTree.css

 /*
  * Copyright 2016 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.
  */
 
 .tree-outline {
     padding: 0;
 }
 
@@ skipping 163 matching lines @@
 }
 
 /* Matched styles */
 
 :host-context(.matched-styles) .tree-outline li {
     margin-left: 0 !important;
 }
 
 .expand-icon {
     -webkit-user-select: none;
-    background-color: #777;
     margin-left: -6px;
     margin-right: 2px;
+    margin-bottom: -2px;
 }
 
 .tree-outline li:not(.parent) .expand-icon {
     display: none;
 }
 
 :host-context(.matched-styles:not(.read-only):hover) .enabled-button {
     visibility: visible;
 }
 
 :host-context(.matched-styles:not(.read-only)) .tree-outline li.disabled .enabled-button {
     visibility: visible;
 }
 
 :host-context(.matched-styles) ol.expanded {
     margin-left: 16px;
 }