chromium/chrome/browser/resources/chromeos/arc_support/overlay.css

/* Copyright 2018 The Chromium Authors
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file. */

/* Hide header for help articles that contains sign-in button, link to apps and
   search bar. Also hide div of class promotion-container that has link to
   YouTube */
.hcfe .promotion-container,
.hcfe > header {
  display: none;
}