Signal-Android/res/drawable/header_search_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/grey_200"/>
        </shape>
    </item>
    <item android:top="1dp">
        <shape android:shape="rectangle" >
            <solid android:color="?attr/search_background" />
        </shape>
    </item>
</layer-list>