src/third_party/devtools/front_end/network/requestHTMLView.css

/*
 * Copyright (c) 2018 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.
 */
-theme-preserve, .html-preview-frame {
  box-shadow: var(--drop-shadow);
  background: white;
  flex-grow: 1;
  margin: 20px;
}