Write code to format cells

Hello

I have a formula in D2 (Sheet1) that spills information depending on what the user enters in [B2:B3]. I would like someone to show me how to write code to format the cells (spilled data range) to have thick outside borders around perimeter and thin on the inside like shown in sample attached. I would also like the cell formatting to disappear when the user clears cells [B2:B3].

Thank you

J