you can try this :
<?xml version="1.0" encoding="utf-8"?>
<shape
xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle">
<solid android:color="#900021df"/>
<size
android:width="10dp"
android:height="5dp"/>
<corners
android:bottomLeftRadius="20dp"
android:bottomRightRadius="20dp"/>
</shape>
it gives this shape: