CMS Made Simple Forums

I am starting to get into CMSMS with great pleasure.*
But the more I get in the more questions I have.
Now I am searching for a way to reduce my header size in http://poisson-clement.fr
In the layout stylesheet I find:

    /* HEADER */
        div#header {
            margin: 0;
            padding: 0;
            background: #999999;           
            color: white;
            text-align: center;
        }
    /* END HEADER */
But there seems no control on the size here.
Is there another template/stylsheet element that I am missing?
regards from france!
SOLVED It depends owhat is put inside , very flexible!

You can always use width: **px; height: **px to make it the size you want...