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

third_party/WebKit/Source/devtools/front_end/ui/slider.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.
  */
 
 .dt-range-input {
     -webkit-appearance: none;
     margin: 0;
     padding: 0;
     height: 10px;
     width: 88px;
     outline: none;
     background: none;
 }
 
-.dt-range-input::-webkit-slider-thumb {
+.dt-range-input::-webkit-slider-thumb, -theme-preserve {
     -webkit-appearance: none;
     margin: 0;
     padding: 0;
     border: 0;
     width: 12px;
     height: 12px;
     margin-top: -5px;
     border-radius: 50%;
     background-color: #4285F4;
 }
 
 .dt-range-input::-webkit-slider-runnable-track {
     -webkit-appearance: none;
     margin: 0;
     padding: 0;
     width: 100%;
     height: 2px;
     background-color: rgba(0, 0, 0, 0.26);
 }
 
-.dt-range-input:focus::-webkit-slider-thumb {
+.dt-range-input:focus::-webkit-slider-thumb, -theme-preserve {
     box-shadow: 0 0 0 2px rgba(66, 133, 244, 0.4);
 }
 
 .dt-range-input:disabled::-webkit-slider-thumb {
     background-color: #bdbdbd;
 }