Signal-Android/app/src/main/res/drawable/keyboard_bottom_bar_background.xml

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape android:shape="rectangle">
            <solid android:color="@color/signal_background_secondary" />
        </shape>
    </item>
    <item android:gravity="top">
        <shape android:shape="rectangle">
            <size android:height="1dp" />
            <solid android:color="@color/signal_inverse_transparent_10" />
        </shape>
    </item>
</layer-list>