Thanks for the unwarranted vote of confidence!
I have the tabs set horizontally and I do not get a scroll bar. I set the tabs to be vertical and one appeared but I could not isolate it.
Then I remembered that when the plugin was first released @benji300 was asked about fonts in the plugin (this thread, above) the reply included
I guess the plugin has no access to the App fonts as is "lives" in an iframe which is decoupled from the App itself.
(my emphasis)
So would the plugin even be aware of custom css in the app itself??? All other colour options appear to have to be customised from defaults in the advanced settings for the plugin.