To make customizing the appearance of RadDropDownTree as easy as possible, the control uses skins. A skin is a set of images and a CSS stylesheet that can be applied to RadDropDown elements (items, images, etc.) and defines their look and feel.
RadDropDownTree is installed with a number of built-in skins:
The Material skin is available for the Lightweight RenderMode only. If you experience visual issues with it, make sure your controls are not using the default Classic mode.