The whole forum is pushed left. Looks like this...
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your /Theme/name/css/ index.css or style.css depends on your version of SMF is got corrupted don't edit those files online in browser or Control panel manager's...
download those files and use a good editor to edit them.
Thats what a forum looks like if the style sheet is miss-named, the path to the style is incorrect or there is no style.
It's a theme problem. How do I uninstall a theme?
use your url/index.php?theme=1 to reset to the default theme and reconfigure or delete theme via admin panel / FTP access