I checked the view source, and saw that the page menu items are unordered list items, with an ID of rmenu2.

<ul id="rmenu2" ....

I want to make that text bold, so I added

ul#rmenu2 li a:link, ul#rmenu2 li a:visited, ul#rmenu2 li a:active, ul#rmenu2 li a:hover, {font-weight: bold;}

to the CSS Inserts field, but no joy.

Any suggestions? Have I just messed up the CSS, or am I going about it wrong?

You may have to add !important or remove the last comma, or both