Hi sgower,
You can use the stylesheet to change the font size of category title. Add bellow css rules to the style file (template.css or custom.css file in css folder of current joomla template) of the your joomla template.
Code:
#kunena.layout ul.kblocktable li .krow-inner .kcol-kcattitle .kthead-title a {
font-size: 16px; /* Current font size, you can change this property */
}
Best regards,
