This is an interesting quirk which I don't remember seeing discussed here before.
I think the problem here is that the title is wrapped inside not just H3 but also a SPAN with class "title" (see the source code). The span will override the H3 settings.
In the default pbase stylesheet [
http://image.pbase.com/styles/gallery2.css] there is a section:
.title {
font-size: 14pt;
font-weight: bold;
text-align: center;
}
This explains why you could change the background but not the font-size. Your font-size setting is being overidden by the SPAN setting of 14pt.
You need to add a .title section to your CSS and set the font-size in that. Or you could probably just combine with H3, i.e.
H3, span.title
{
...
}
But check for side effects, I don't know if .title is used anywhere else.