packages/SystemUI/res/drawable/control_background.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
/*
* Copyright 2020, The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*     http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
-->
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
  <item
      android:id="@+id/background">
    <shape>
      <solid android:color="@color/control_default_background" />
      <corners android:radius="@dimen/control_corner_radius" />
    </shape>
  </item>
  <item
      android:id="@+id/clip_layer">
    <clip
        android:clipOrientation="horizontal"
        android:drawable="@drawable/control_layer"/>
  </item>
</layer-list>