chrome/android/java/res/drawable-v31/section_tab_background.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2022 The Chromium Authors. All rights reserved.
     Use of this source code is governed by a BSD-style license that can be
     found in the LICENSE file. -->

<selector xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
  <item android:state_selected="false">
    <org.chromium.components.browser_ui.widget.SurfaceColorDrawable
        android:shape="rectangle"
        app:surfaceElevation="@dimen/section_tab_selected_bg_elevation">
      <corners android:radius="@dimen/section_tab_background_corner_radius"/>
    </org.chromium.components.browser_ui.widget.SurfaceColorDrawable>
  </item>
<item android:state_selected="true">
    <org.chromium.components.browser_ui.widget.SurfaceColorDrawable
        android:shape="rectangle"
        app:surfaceElevation="@dimen/section_tab_bg_elevation">
      <corners android:radius="@dimen/section_tab_background_corner_radius"/>
      <stroke android:width="@dimen/section_tab_bezel_width" android:color="@android:color/transparent" />
    </org.chromium.components.browser_ui.widget.SurfaceColorDrawable>
  </item>
</selector>