I often find that sometimes the smallest things that were simple in regular HTML are frustratingly complex in CSS. Take, for example, centering a div. You can float it right, float it left, but there is no center. Using text-align: center does not center it either, it just makes any text inside of it centered.
It turns out it is very simple to do. The key is that you must specify a width for your div, either using an exact pixel width, a percentage, or some other measure like em units. Once you set the width, you just have to add left and right margins set to auto, and the div will be centered inside of the container it is in.