RadControls for ASP.NET AJAX
The visual appearance of Telerik RadControls for ASP.NET AJAX is defined through "skins". A skin consists of a CSS file and image files (which are optional). Telerik RadControls for ASP.NET AJAX come with a set of built-in skins which are embedded in the Telerik.Web.UI assembly and ready to be used. Developers can use the built-in skins as they are, or customize them.
Using a skin
To use a skin you just need to set the Skin property of the control to the designated skin name.
Keep in mind that skin names are case-sensitive. You can set the Skin property declaratively, in design time or from code-behind.
If you are using a custom skin, you need to set the EnableEmbeddedSkins property to false.
If you don't do that, the control will try to register an embedded skin with the specified name and will fail with an exception.
For more information you can check the How skins work and Skin registration topics.
Setting the skin from design time
To set the skin in design time you need to follow these steps:
Select the control of interest by clicking it.
Open its properties (either from the context menu or by pressing F4).
Find the Skin property in the property grid (it is located in the "Appearance" category).
To use a built-in skin
Open the drop-down control which contains all built-in skins.
Select a value from the drop-down to set that skin.
To use a custom (user-defined) skin
Register the CSS file(s) of the skin to the Page (unless they are placed in an ASP.NET theme folder)
Set the EnableEmbeddedSkins property to false
Type the name of the skin in the text box
Setting the skin declaratively
To set the skin declaratively you need to set the Skin attribute of the control tag. Keep in mind that it is case-sensitive.
<telerik:RadSlider ID="RadSlider1" Skin="Outlook" runat="server" />
Setting the skin from code-behind
To set the skin from code-behind you need to set the Skin property of the control to the designated value:
Setting the skin globally from web.config