DevTools: Modify shadow-editor canvas colors to work better with dark theme

third_party/WebKit/Source/devtools/front_end/ui/cssShadowEditor.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.
  */
 
 :host {
     -webkit-user-select: none;
     padding: 4px 12px 12px 12px;
 }
@@ skipping 47 matching lines @@
 }
 
 .shadow-editor-button-left:hover, .shadow-editor-button-right:hover {
     box-shadow: 0 1px 1px rgba(0, 0, 0, 0.1);
 }
 
 .shadow-editor-button-left:focus, .shadow-editor-button-right:focus {
     background-color: #eeeeee;
 }
 
-.shadow-editor-button-left.enabled, .shadow-editor-button-right.enabled {
+.shadow-editor-button-left.enabled, .shadow-editor-button-right.enabled, -theme-preserve {
     background-color: #4285F4;
     color: #ffffff;
 }
 
-.shadow-editor-button-left.enabled:focus, .shadow-editor-button-right.enabled:focus {
+.shadow-editor-button-left.enabled:focus, .shadow-editor-button-right.enabled:focus, -theme-preserve  {
     background-color: #3B78E7;
 }
 
 .shadow-editor-text-input {
     -webkit-appearance: none;
     box-sizing: border-box;
     width: 52px;
     height: 24px;
     margin-right: 8px;
     padding: 3px 7px;
     line-height: 16px;
     border: 1px solid rgba(0, 0, 0, 0.14);
     border-radius: 2px;
     background-color: #ffffff;
     color: #333;
     text-align: right;
 }
 
-.shadow-editor-text-input:focus {
+.shadow-editor-text-input:focus, -theme-preserve {
     border-color: #4285F4;
 }
 
 .shadow-editor-text-input.invalid {
     border-color: #E67C73;
 }