With RadTabStrip you can customize the look and feel of each single tab. RadTab objects have a number of properties whose value is the name of a CSS class (CssClass, SelectedCssClass,DisabledCssClass, HoveredCssClass, ChildGroupCssClass, OuterCssClass etc). These properties let you alter the appearance of individual tabs in the tab strip without using a custom skin.
The following links explains more on this topic.
Custom CSS Classes
Setting the CSS Class of Tabs