There is an open issue (#151) and an emailed request about customising the CSS. Is it possible to pass a custom css url into the TimelineJS options - and do any of the layout customisations listed in their FAQ apply?
Great question - at the moment this still isn’t possible (the issue you link to is still open). It would be a relatively easy fix (a few hours I imagine) but needs some time to do it.
The TimelineJS layout options aren’t supported at the moment I believe. Again wouldn’t be hard to add.