res/drawable/popup_background_selected.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <corners
        android:topLeftRadius="28dp"
        android:topRightRadius="28dp"/>
    <solid android:color="@color/accent_color" />
</shape>