Hi Dmitry,
Thanks for your interest in Syncfusion products.
HTMLUI Control does not support cellpadding and cellspacing attribute.
It supports only CSS attributes.
Please refer the online documentation on the following link for further details
http://help.syncfusion.com/UG_82/WindowsFormsUI_HTMLUI/PaddingCSS.htmlPlease let us know if you have any concern.
Regards,
Lokanath.E