The type on 1 of my sites is permanently bold?

I have a multisite, buddypress, pro site installation. In that installation, my main site holds the pro site activation/configuration. I noticed about 2 days ago that the type face on every page of that site, including the buddypress has changed to permanent bold. It is not what I want at all. I can't see anyway to change it.

Check out this page as an example:

I do have the My CSS plugin, and I am using Studio theme. Thanks in advance! Linda @iempoweru