chromium/chrome/browser/ui/android/quickactionsearchwidget/java/res/drawable/quick_action_search_widget_background.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
Copyright 2021 The Chromium Authors
Use of this source code is governed by a BSD-style license that can be
found in the LICENSE file.
-->

<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <solid android:color="@color/default_bg_color_baseline" />
    <corners android:radius="@dimen/quick_action_search_widget_background_radius" />
</shape>