The new Blocs tab uses three classes to adjust the settings.
nav-tabs
This is used mostly for setting the length of the tabs and lines (strokes)
nav-tabs .nav-link
This is acually the list and links in the tabs. It is used to adjust these areas.
nav-tabs .nav-item.show .nav-link, .nav-tabs .nav-link.active
I’m not sure what all these are for but the most common use is to set the active tab. Maybe change the background color or other atributes.
Casey