RadControls for ASP.NET AJAX
RadTabStrip for ASP.NET AJAX has a similar rendering to its predecessor, RadTabStrip "Classic". Below is a table which shows the mapping between the CSS classes:
RadTabStrip "Classic" selector
RadTabStrip for ASP.NET AJAX CSS class
If your existing skin includes overlapping tabs, minor changes could be necessary (apart from changing the CSS classes) - the RadTabStrip for ASP.NET AJAX does not position its tabs relatively and thus a negative margin will not work as expected. The overlapping effect is achieved by using the two CSS classes of rtsBefore and rtsAfter, which are applied on the tabs that are next to the currently selected tab.