chromium/components/browser_ui/widget/android/java/res/drawable/bottom_sheet_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="@macro/default_bg_color" />
    <corners
        android:topRightRadius="@dimen/bottom_sheet_corner_radius"
        android:topLeftRadius="@dimen/bottom_sheet_corner_radius" />
</shape>