We use this theme as it corresponds to the color scheme of our main website.
In my case, I implemented a quick "rough" fix by myself yesterday. I changed themes\soclean\theme.css. At the top of the file, we have this:
.yafnet td {
font-family: Verdana,Arial,Helvetica,sans-serif;
font-size: 8pt;
color:#404040;
}
I set font-size to 10pt. This also increases the font overall, not only the font of posts. But when I look at this larger font in all parts of forum, my eyes are relaxing now - after that tiny 8pt font!