app/src/main/res/drawable/gradient.xml

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@android:color/white" />
    <item>
        <shape>
            <gradient
                android:angle="225"
                android:startColor="#FF0000" />
        </shape>
    </item>
    <item>
        <shape>
            <gradient
                android:angle="0"
                android:startColor="#000000" />
        </shape>
    </item>
</layer-list>