chromium/chrome/android/java/res/drawable/tab_close_button_bg.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"
    android:shape="oval">
  <size
      android:width="24dp"
      android:height="24dp" />
  <solid android:color="@color/modern_white" />
</shape>