I created a custom control which extends HTMLTableCell to make it clickable.

the code is here

[ToolboxData("<{0}:ClickableHTMLTableCell runat=server></{0}:ClickableHTMLTableCell>")]
    [ParseChildren(false)]
    public class ClickableHTMLTableCell : HtmlTableCell, IPostBackEventHandler
    {... }

however, in visual studio, the control in designer preview shows only a big gray box, no content, no styles in preview.

I guess there should be an attribute to control the preview, but I don't know how. Can some one help me?