Devtools [CustomFormatters]: Fix appearance of an arrow on the mac

Source/devtools/front_end/components/customPreviewSection.css

 /*
  * Copyright (c) 2015 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.
  */
 
 .custom-expandable-section {
     display: inline-flex;
     flex-direction: column;
 }
 
 .custom-expandable-section-header::before {
     -webkit-user-select: none;
     background-image: url(Images/toolbarButtonGlyphs.png);
     background-size: 352px 168px;
     opacity: 0.5;
     content: "a";
     width: 8px;
     margin-right: 4px;
     padding-right: 2px;
     color: transparent;
     text-shadow: none;
 }
 
+@media (-webkit-min-device-pixel-ratio: 1.5) {
+    .custom-expandable-section-header::before {
+        background-image: url(Images/toolbarButtonGlyphs_2x.png);
+    }
+} /* media */
+
+
 .custom-expandable-section-header::before {
     background-position: -4px -96px;
 }
 
 .custom-expandable-section-header.expanded::before {
     background-position: -20px -96px;
 }
 
 .custom-expandable-section-standard-section {
     display: inline-flex;
 }