Our Client requirement is to hide the X Close button on RadSpell Dialog. 

Added below code to hide from CSS which works fine:

 .RadWindow_Default .rwControlButtons A
        {
            display: none !important;
        }   
.RadWindow .rwControlButtons A
        {
            display: none !important;
        }   

Now the requirement is when CSS is disabled, user should not see the Close link.

"There is a 'Close' link that appears when CSS is disabled within the dialog. This link does not appear on the page with CSS enabled. Please find the attachment.

Is there any way we can hide/disable this X Close link/button from JavaScript or CodeBehind.

Thanks