In some scenarios you may want to use a built-in (embedded) skin, but make some minor adjustments to it. In such cases it is easier and more convenient to override styles from the embedded skin, rather than to use a complete custom skin.
In order to override a style from a built-in skin, you will have to find out the CSS rule, which must be overridden, and then construct a new CSS rule with a higher specificity. To accomplish this, it will be useful to have a general idea about the control's HTML output and CSS classes. Basic CSS knowledge is required as well.
Each Telerik control documentation includes a help article, which lists the CSS classes of the control and describes their usage. For example the RadCalendar CSS class list states that "rcWeek is a class applied to the
The built-in (embedded) Telerik controls skins can be reviewed as ordinary CSS files and images - they are provided in the /Skins/ subfolder located in the Telerik UI for ASP.NET AJAX installation folder (if you have used an executable installer), or in the installation ZIP. The file structure is as follows:
/ Skins / ControlName.css - the base stylesheet of a given Telerik control
/ Skins / SkinName / ControlName.SkinName.css - the skin CSS of a given Telerik control
/ Skins / SkinName / ControlName / ...images... - the skin images of a given Telerik control
/ Skins / Common / ...images... - images used by various controls and/or skins
/ Skins / SkinName / Common / ...images... - images used by various controls
The easiest way to discover which CSS rule is responsible for a given control style applied in the browser is to use some web developer tool such as Firebug for Firefox or Web Developer Toolbar for Internet Explorer. Such tools help inspect the HTML output and CSS styles instantly and even allow experiments and changes on the fly. Another useful opportunity these tools provide is to learn about the Telerik controls HTML rendering.
The CSS knowledge required to modify (override) embedded skins includes familiarity with the different types of CSS selectors and the notion of CSS specificity.
Articles about CSS specificity:
Here is a blog post, which extends the information above with an example about overriding a RadGrid skin.
Also you can refer the PSD files for the obsolete controls' skins and some specific custom skins using the portal below: