res/layout/activity_captive_portal_login.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context="com.android.captiveportallogin.CaptivePortalLoginActivity"
    tools:ignore="MergeRootFrame" >

    <LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

      <FrameLayout
          android:layout_width="match_parent"
          android:layout_height="4dp" >

        <!-- Eliminates ProgressBar padding by boxing it into a 4dp high container -->
        <ProgressBar
            android:id="@+id/progress_bar"
            style="@android:style/Widget.Material.Light.ProgressBar.Horizontal"
            android:indeterminate="false"
            android:max="100"
            android:progress="0"
            android:layout_gravity="center"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
      </FrameLayout>

      <FrameLayout
          android:layout_width="match_parent"
          android:layout_height="match_parent" >

        <androidx.swiperefreshlayout.widget.SwipeRefreshLayout
            android:id="@+id/swipe_refresh"
            android:layout_width="match_parent"
            android:layout_height="match_parent">

          <WebView
              android:id="@+id/webview"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:layout_alignParentBottom="false"
              android:layout_alignParentRight="false" />
        </androidx.swiperefreshlayout.widget.SwipeRefreshLayout>

        <!-- The layout is focusable and clickable to prevent interaction through it. -->
        <FrameLayout
            android:id="@+id/downloading_panel"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:alpha="0.5"
            android:background="#000000"
            android:visibility="gone"
            android:clickable="true"
            android:focusable="true"
            android:gravity="center">

          <ProgressBar
              android:id="@+id/download_in_progress"
              android:background="?android:attr/colorBackground"
              android:layout_centerInParent="true"
              android:layout_gravity="center"
              android:padding="20dp"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content" />
        </FrameLayout>

      </FrameLayout>
    </LinearLayout>
</FrameLayout>