I've moved the Welcome control on my masterpage, and now the menu items do not render correctly. I've tried to find the appropriate CSS class name that is causing the problem, with no success.
What class names control the height of the menu items?
To identify the classes you need to adjust (or probably re-override a style you overrode for your masterpage) you can use the Internet Explorer Developer Toolbar (hit F12 on your keyboard). Be sure to hit it after you open the window so the toolbar sees the menu opened. Then use the selector to select the areas you need to work on.
First you wanna find the class in corev4 css that controls the menu items
Like this http://screencast.com/t/Wnz1BoVw
I have added a background-color - now you wanna do your own thing.
When you have your changes in place - put them in another css file and place the after the corev4 (should not be a problem as corev4 is the first css to be loaded)
Best of luck