I'm sorry, but I have to correct my previous statements:

- the ~/.config/geany/geany.css file DOES have an influence on the tab styling, you have to close Geany and restart it to take effect.

  The content of the CSS file I included can be added at the end of geany.css.

  Apologies,

No problem, I was just about to report that.  Your code works.  Only thing -- and it's trivial -- would be to get rid of the little blue bar now.   Thanks Lucas.