Discussions with many nested replies have the problem that the
deepest comments become very narrow because of the indention.
Widening the browser window leads to the higher-level comments
being too wide to read comfortably.
I suggest to add a style parameter:
Typographic conventions are to restrict a line length to about 75
characters, which would typically be 37.5em. With 60em you
might improve the current situation without too much offending
users that like the current situation.