chromium/chrome/android/java/res/drawable/card_container_background.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
Copyright 2022 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">
    <corners
        android:radius="12dp" />
    <solid android:color="@color/baseline_neutral_variant_80_alpha_15"  />
</shape>