How to move site height 25 pixels down?

First, excuse my poor english, but I try to be as objective as possible. I created a '<DIV>' at the top of the page to accommodate two menu buttons on a plugin for Wordpress that I acquired. However, this <div> occupies the same area as the top menu overlapping each other. I wonder if it is possible, using custom CSS to move around the template 15 pixels away from the top edge of the screen to accommodate this <div> further without compromising the template layout?