rsb_default_thumb.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="oval">
    <solid android:color="@color/platform_gray7" />
    <stroke
        android:width="1dp"
        android:color="@color/platform_gray7" />
</shape>