It seems the width of the forum keeps a maximum of ~1.260 px, no matter what width is set in admin center (theme settings). Is there a chance to change this? Or do you see problems if I edit the template files so the forum expands up to... say 1.900 px width?
Index.css:
max-width: 90em;
it's one of the firsts lines.
The css is there because usually read very long lines is more difficult (come back and find the "next" line becomes tricky in long texts because by the time you are back at the left side of the screen you may have lost the position and you may end up skipping a line or reading again the one that you just finished), but you can remove that and make it as wide as you like. ;)
The easiest way is just to remove or comment out the line.
Thanks! :)