That's not really enough code. We'd need to see your HTML, too. See if you can post a full working example.
I wouldn't be using position: absolute there, however. 100% width is easy enough, but it sounds like you want a sticky footer, or a page that is always at least 100% tall. (It's pretty dangerous not to allow overflow, though, as content on some very small devices is unlikely to fit on the screen all at once.)
Here's an explanation of how to do 100% height: