chromium/chrome/android/webapk/shell_apk/res/values-night-v17/styles.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
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.
-->

<resources xmlns:tools="http://schemas.android.com/tools">
  <style name="SplashTheme" parent="@android:style/Theme.Holo">
    <item name="android:windowActionBar">false</item>
    <item name="android:windowNoTitle">true</item>
    <item name="android:windowBackground">@color/dark_background_color_non_empty</item>
  </style>
</resources>