DevTools: Fix media query labels partially visible on Device Mode page.

third_party/WebKit/Source/devtools/front_end/emulation/mediaQueryInspector.css

 /*
  * Copyright 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.
  */
 
 /* Media query bars */
 
 .media-inspector-view {
     height: 50px;
 }
 
 .media-inspector-marker-container {
     position: relative;
     height: 14px;
     margin: 2px 0;
 }
 
 .media-inspector-marker {
     position: absolute;
     top: 1px;
     bottom: 1px;
     white-space: nowrap;
+    z-index: auto;
 }
 
 .media-inspector-marker:hover {
     top: -1px;
     bottom: -1px;
     opacity: 1;
 }
 
 .media-inspector-marker-max-width {
     background-color: hsl(207, 90%, 77%);
@@ skipping 28 matching lines @@
 }
 
 /* Media query labels */
 
 .media-inspector-marker:not(:hover) .media-inspector-marker-label-container {
     display: none;
 }
 
 .media-inspector-marker-label-container {
     position: absolute;
+    z-index: 1;
 }
 
 .media-inspector-marker-label-container-left {
     left: -2px;
 }
 
 .media-inspector-marker-label-container-right {
     right: -2px;
 }
 
 .media-inspector-marker-label {
     color: #222;
     position: absolute;
     top: 1px;
     bottom: 0;
     font-size: 12px;
     pointer-events: none;
 }
 
 .media-inspector-label-right {
     right: 4px;
 }
 
 .media-inspector-label-left {
     left: 4px;
 }