Signal-Android/app/src/main/res/layout/add_members_activity.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_gravity="center"
        android:orientation="vertical">

        <org.thoughtcrime.securesms.components.ContactFilterToolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:elevation="4dp"
            android:minHeight="?attr/actionBarSize"
            android:theme="?attr/actionBarStyle"
            app:contentInsetStartWithNavigation="0dp"
            app:navigationIcon="@drawable/ic_arrow_left_24" />

        <fragment
            android:id="@+id/contact_selection_list_fragment"
            android:name="org.thoughtcrime.securesms.ContactSelectionListFragment"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />

    </LinearLayout>

    <com.dd.CircularProgressButton
        android:id="@+id/done"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_marginEnd="16dp"
        android:layout_marginBottom="16dp"
        android:textColor="@color/white"
        app:cpb_colorIndicator="@color/white"
        app:cpb_colorProgress="?colorAccent"
        app:cpb_cornerRadius="28dp"
        app:cpb_selectorIdle="@drawable/progress_button_state"
        app:cpb_textIdle="@string/AddMembersActivity__done"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent" />
</FrameLayout>