CSS class "selected" should be assigned to selected items in the top-menu
Currently you can't address the selcted menu item of the top-menu with CSS because there is no class "selected" assigned to the active tab. Some plugins are doing that already for their entries in the top-menu and the project menues are also working in this way. This should also be implemented for the redmine core.
It will increase redmines "themeability" and will bring more consistency in the css design logic if menus are handled similar.