There does not seem to be any direct way, since document. styleSheets does not contain the user agent style sheet. On the other hand, Firefox Web Developer Extension has, in the CSS menu, an option for disabling Browser Default Stylesheet. Anyway, there is a markup way, though I’ m not sure whether you like its implications. TreeGrid SpreadSheet is an application core for building online ( web based) spreadsheet software like MS Excel, OpenOffice Calc or Google Sheets. It is complex and fully customizable web spreadsheet with huge features set.
user style sheets in dhtml menu
More information. Create presentations using cascading style sheets and dhtml.