[Lynne]

The "Basic Information" font-size in that image should be set by this CSS:

.profile_content .subsectionhead, #postlist .subsectionhead {
    padding: {vb:math {vb:stylevar padding}/2} 0;
    clear:both;
    font-weight: bold;
    font-size: {vb:math {vb:stylevar font.fontSize}+4}px;
}

So, in part, it is set by the regular font-size stepped up by 4. You can add something to the additional.css template to change it manually, like:

.profile_content .subsectionhead, #postlist .subsectionhead {
    font-size: 15px;
}