By default, DITA2Go does not try to assign CSS classes to DITA elements (unless you set [CSS]UseCSS=Yes; see §31.4 Specifying CSS file and link options).
To direct DITA2Go to provide an outputclass attribute for elements that allow this attribute:
[DITAOptions]
; UseOutputClass = No (default when [CSS]UseCSS=No)
; or Yes (default when [CSS]UseCSS=Yes)
UseOutputClass = Yes
When UseOutputClass=Yes, DITA2Go includes an outputclass attribute where allowed. The value of the attribute is the [ParaClasses] or [CharClasses] assignment (if any) for the format mapped to the element, otherwise the name of the format mapped to the element. See §31.7 Assigning CSS classes.
Note: To include outputclass attributes, make sure your configuration file does not specify [CSS]WriteClassAttributes=No.
The only way to include an outputclass attribute in the root element is with a DITATopicOutputclass marker: place the marker anywhere in the topic, and make the content of the marker the value of the outputclass attribute.