samples/wearable/Notifications/Application/src/main/res/drawable/selected_background.xml

<?xml version="1.0" encoding="utf-8"?>

<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <padding
        android:top="4dp"
        android:bottom="4dp"
        android:left="4dp"
        android:right="4dp"/>
    <stroke
        android:width="4dp"
        android:color="@android:color/holo_blue_bright" />
</shape>