Ah, you want the CSS selector ‘active’.
On your CSS stylesheet you have the lines that govern the element such as .nav or #navbar li, something like that. You want to add a few lines of code to handle the separate treatment of the active element.
For a nav bar with the div class ‘menu’ you would have something like
.menu li { some css goes here } and you would want to add another line such that .menu li:active { has some different styling }
If you have a parent/child relationship between your navigation elements you might want to take a look at this thread to head off any problems with your styles carrying over into subsequent ul/li elements.