packages/SystemUI/res/drawable/rounded_bg_bottom_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="?android:attr/panelColorBackground" />
    <corners
        android:bottomLeftRadius="?android:attr/dialogCornerRadius"
        android:topLeftRadius="0dp"
        android:bottomRightRadius="?android:attr/dialogCornerRadius"
        android:topRightRadius="0dp"
        />
</shape>