Click on the advanced menu and then click on the ribbons tab which includes: image, width, and height. 

A ribbon is a tiny image that goes on the left or right of the button.

Here is how to add ribbons:

Step 1: Get into advanced mode.

Step 2: Click on the ribbons menu (A). 

Step 3: Upload or search for an image (B). 

Step 4: Adjust the width and height (C and D). 

Step 5: Click on the left and right tabs to adjust the offset x and offset y (E).