Just for being more precise - you have to edit these templates:
Have you take a look at the Basic skin theme for miniBB
I suppose, this is what you need, and you could start/gain many ideas from it... you could also get templates and CSS of this theme from miniBB demo (right mouse click -> Save File As):main_forums_cell.htmlmain_last_discuss_cell.htmlmain_topics_cell.htmlbb_old_style.css
The other templates could be saved from the same URL, they all are named like default miniBB's templates.
Save all these files to your forum folder or templates folder, and then set in setup_options.php