BayernMessenger/vector/src/main/res/drawable/bg_room_item.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:state_checked="true">
        <shape>
            <solid android:color="@android:color/white" />
            <corners android:radius="4dp" />
        </shape>
    </item>
    <item>
        <shape>
            <solid android:color="@android:color/transparent" />
        </shape>
    </item>

</selector>