Which RoboHelp version and which layout? You have to set it through the CSS, but exactly where you do it depends on the layout you're using.
Thanks for getting back to me. I'm using RoboHelp, 11 and I'm using the Theme_1 Standard layout. I looked in the CSS and probably just didn't see where that could be modified.
For that layout:
If you set the font-size in these selectors in the CSS, the entire TOC is updated.
Thanks William; I really appreciate the help!