RadTreeMap uses skins to control its overall look-and-feel. A skin is a set of images and a CSS stylesheet that can be applied to the control elements (items, images, etc.) and defines their look and feel. To apply a skin to RadTreeMap set its Skin property, either using the properties pane or the control's Smart Tag.
RadTreeMap is installed with a number of preset 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.