chromium/android_webview/tools/system_webview_shell/apk/res/values-v29/styles.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2019 The Chromium Authors
     Use of this source code is governed by a BSD-style license that can be
     found in the LICENSE file. -->

<resources>
  <style name="ShellTheme" parent="Theme.AppCompat.DayNight.NoActionBar">
    <item name="android:forceDarkAllowed">true</item>
    <item name="android:isLightTheme">true</item>
  </style>
</resources>