single_tab_thumbnail_background.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
Copyright 2023 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">
  <solid android:color="@color/thumbnail_placeholder_on_primary_bg"/>
  <stroke
      android:width="1dp"
      android:color="@macro/divider_line_bg_color" />
  <corners android:radius="@dimen/single_tab_thumbnail_radius" />
</shape>

chromium/chrome/browser/single_tab/android/java/res/drawable/single_tab_thumbnail_background.xml