Are you using a "css reset", i.e. removing all padding and margin at the top of your style sheet (assuming the attached style sheet is not your full style sheet).
If not, remove the minus margin and add the following to the top of your css file:
* { margin:0; padding:0; }
If that works and removes the space then I would advice you to read about css reseting since using the wildcard (*) is not a good way to do it.