But when I change the font-size nothing happens. So I guess that's being set somewhere else?

That's exactly right. When you use the font settings on the Appearance → Custom Design → Fonts page, those settings are very specific. To override them, you can add an !important declaration. Here is an example:

.nav a {
     font-size:16px !important;
}

But when I change the font-size nothing happens. So I guess that's being set somewhere else?

.nav a {
position:relative;
color:#060606;
display:block;
z-index:100;
padding:70px 20px 15px;
line-height:18px;
text-decoration:none;
text-shadow:0 1px 0 rgba(255,255,255,0.8);
min-width:60px;
font-size:16px;
font-weight:normal;
border:1px solid #D6D7D7;
border-width:0 1px 0 0;
}

TY!

Van

It seems, for example, that I am able to change the h3 font size for the entire blog:
h3 {font-size: 1.6em;}

But when I try to change individual things, nothing happens:

#comments h3 { color:#333; font-weight:bold; margin:30px 0; }

#main h3.section { background: url(images/strips.png) repeat; padding:10px 15px; line-height:1em; font-weight: bold; margin-bottom: 25px; }

I'm new to CSS and no doubt doing it a bit wrong, but I'm grateful for any pointers you can offer.

TY!

I found 41 "font-size:" references in the style sheet for Delicious Menu.

When I changed a few of them in the CSS Style Editor it worked well... but most of them "don't work" -- could they be overridden somewhere else? Or overridden by the custom font option itself?

TY!!

My site is:
http://iRez.me

I'm using the lovely WooThemes Delicious Magazine and just added the Font/CSS upgrade. I picked the nice handwritingish font FF Market for the headings - I like the feel of it a lot, but there are places it's bolded and hard to read and other places it feels like it should be a bit larger or smaller.

Anyway, I'll try your advice to rowaidaabdelaziz, ty!

My suggestion would be to copy the entire styesheet into a plain text file and then do a search for "font-size:" (without the quote marks and then you can pull out those selectors, add them to the CSS edit window and adjust the sizes as you desire.

I'm a little curious though as in my opinion, Piano Black, the theme on the site referenced in your post above, has text that I, as a web designer, consider too small, and I would be going the other way with the font sizes.