I would like to modify the text-size of the message box (new threads and posts) but can´t find any settings for this.
Where can I adjust this?
This you have to adjust in the "modules/eBoard/templates/header.html"-file.
Change on line 92 the setting:
Zitatfont-size : 10px;
to your needs (e.g. font-size : 12px; for 12 pixels).