Do anyone of you have a clue how to make a menu like the one that the picture shows. I want a menu that changes color when hovered. Wordpress solves the change of color when a menu button is active, with the current class, but how do I make that little arrow on an expandebel button? If the menu buttons where just squares the a:hover effect would work just fine, but how can I add that little arrow?
Hi shedda. Welcome to SitePoint. 
You could either do that with a background image, or even with a little bit of pseudo content, as demonstrated here: http://www.yuiblog.com/blog/2010/11/22/css-quick-tip-css-arrows-and-shapes-without-markup/