I read in some post somewhere else that this doesn't work. I tried and tested it, and found that it does not work. The way that I tested it was that I added the bold to the regular text, and not to the hover headline, and there is no difference. If the bold worked, it would be obvious as soon as I ran the cursor over the text. The thread that I read says the header.php is stepping on the font weight property. Here is that link to that thread. http://forum.bytesforall.com/showthread.php?t=2045
It could be that the header.php has already inserted bold as default, but I don't know for sure.