RadControls for ASP.NET AJAX
Every skin provides a default icon that appears in the RadDock title bar for custom commands. Typically, however, you will want to change this icon to a more meaningful image.
To modify the image that appears as a custom command's icon, you need to follow these steps:
Define a CSS class that identifies a background image to represent the custom command. You can use a separate CSS file and link to it, or you can define the CSS class in the <head> tag of the Web page. The CSS class you define is applied to the <a> element for the command on the rendered Web page.
width: 15px !imoprtant;
background: url(../MyImages/CustomCommand.gif) !imoprtant;
Set the CssClass property of the command to your new CSS class:
<telerik:raddock runat="server" id="RadDock1" text="Custom Command">
If the custom command has two states (when using Telerik.Web.UI.DockToggleCommand), set the AlternateCssClass property of the command to supply an image for the alternate state.