Thank you for the suggestion. We will take it into consideration when extending the control's functionality.
You can use image sprite for the Icons (or the button's image) in the following way:
Set a CSS class to the Icon, e.g. PrimaryIconCssClass="classIcon";
In the CSS class set the background-image and the background-position for the primary icon.
Set HoveredCssClass and PressedCssClass to the RadButton control
Cascade through the hovered and pressed classes to set the background positions for the hovered and pressed state, respectively.
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