chromium/chrome/android/java/res/drawable/bg_circle_tab_strip_button.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="oval">
  <!--  Set button background to 32 dp diameter for tab strip redesign buttons-->
  <size
      android:width="32dp"
      android:height="32dp" />
  <solid android:color="@color/modern_white" />
</shape>