Here you go:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/rounded_orange">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_margin="8dp"
android:text="Text"/>
<RelativeLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="32dp"
android:background="@drawable/rounded_green">
</RelativeLayout>
</RelativeLayout>
Where the drawables (only green shown here) are laid out like this:
<?xml version="1.0" encoding="UTF-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="rectangle">
<solid android:color="#0F0"/>
<corners android:radius="16dp"/>
</shape>
If you need help applying the custom layout.xml file to your dialog, read up on 'Creating a Custom Dialog' in the official docs of Dialog.