I was going through the similar problem where I needed to create a fixed div but it should take the required space and shouldn't overlap the content. I figured a way to make it possible easily although you may need to write more code. Here is how you can do it:

• Create 2 divs for each unit use one div to acquire the required space and another to show the content. Basically overlap the div that takes up the space for you with the div you intend to display.

Hope this helps.