Make the background stick when changing the size on the text
 

I want to make the background stick so that when you resize the text using "ctrl +" og "ctrl -" the picture will not follow.

What is happeingn now is that the picture is resizing and the outside of the picture would turn white and make the web-page unusuable since the text is is white.

Is there any way to make the background stick no matter what, and make only the text smaller/larger