[AccessD] Formatting the text of a tab caption

YATAAICFO (yet another thing about Access I cannot figure out): in the
current app I have succeeded a couple of times in making the tab caption
bold, but I can't remember how I did it. The client likes it and now I want
to do it on numerous other tabbed pages, but when I select the tab the
formatting toolbar is all unselectable. And yet I succeeded in at least a
couple of tabbed controls.
Can anyone tell me how to do it? Precisely what causes the controls on this
toolbar to become unselectable at times, and selectable at other times?
Obviously, this is low on the list of priorities, but it miffs me doubly
because I have done it at least twice in this app, and cannot seem to do it
again.
TIA,
Arthur