Keep your styles in your external stylesheet, this is the correct way to format it
#topmenu {
position: static;
top: 0;
}
<ul id="topmenu">
As position: static is the default positioning used for html elements then you don't need to specify it anyway and you also don't need the top: 0 unless you are positioning absolutely or relatively.
If you want the menu to stay fixed when scrolling then you would use position: fixed; top: 0;
