session-android/res/drawable/prominent_filled_button_medium_background.xml

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

    <solid  android:color="?colorAccent" />

    <corners android:radius="@dimen/medium_button_corner_radius" />

    <stroke android:width="@dimen/border_thickness" android:color="?colorAccent" />
</shape>