Normally, you use EM or PT for font sizes. To make them not scroll, use PX.

If you want to code everything well, you want to make everything work at any size. All of my sites work on both super small screens and super large screens. Most of the time using a % is the best way to go, unless if you want a specific value, such as the width of an image.

And while you are at it, try not to use div's at all. Scary thought, huh?