Exports only the markup structure
The Markup Only option adds only the markup structure in the exported HTML. Enabling this option will "break" the page. It's available for developers who want to write their own CSS.
Normal HTML with user defined a "group" class
Markup only where user only added a "group" class
Only the id, classes, attributes that you have defined for each element will be exported.
If you want to completely remove the page styles remove the styles token from the page template.