@Tech you should first download Bootstrap (http://getbootstrap.com/getting-started/ ), then upload bootstrap.css or bootstrap.min.css to your server (I uploaded it on core/skin/). After that you should add the file call on core/views/default.master.php in the <head> section.
<link rel="stylesheet" href="http://www.forumapicoltura.com/core/skin/bootstrap.css">
I edited the Bootstrap CSS file to change the width of the .col-md-6 (so you'll have to search in the CSS file for that id and change its width to 30%). Like this:
Then you can try uploading my file to your core/channels/ folder and see what happens. I also modded the Bootstrap .thumbnail CSS id in order to add the background image that is changing on mouse-hover. If you view-source in my forum you can find the definitions in the code. If you have any problem let me know!
I have to say that this modification is not a well done mod. It has bugs... if you resize the browser window you can see them. The grid is not working as great as it should. But for now I'm happy with it. :)