You need to create a drawable
with layer-list
with two items as rectangle shape . one for the background
and other as stroke
with some margin
.
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
<item>
<shape android:shape="rectangle">
<gradient android:startColor="#54d66A" android:endColor="#54d66A" android:angle="270"/>
<size android:height="20dp" android:width="20dp"/>
</shape>
</item>
<item android:bottom="2dp" android:left="2dp" android:right="2dp" android:top="2dp">
<shape android:shape="rectangle" >
<stroke android:width="2dp" android:color="#ffc0c0c0" />
</shape>
</item>
</layer-list>
And , set this drawable as state_checked
background.