Image and the background style can't deviate synchronously.

Dear all.

I come across one question just as the title depicted,I changed the style(which image is a picture) of a piece of area  in the mushup, then put a panel on the area ,place some image on the panel against the backage , it work well on IE with 100% size,but when enlarge the page,the  image and the background style can't  deviate synchronously.

Anyone can help me ?