The month view of the calendar doesn't have appropriate css.
We should copy some css from an existing project to make it look nice.
Also the calendar is wider than the content column on the standard default site page template.
Could use some enhancements but is not totally awful.
That one can indeed use some css love.
Though I think that the issue is about the mod_calendar and then the calendar view inside.
Actually I wouldn't be surprised if the calendar view is now quite broken due to the introduction of bootstrap.
See: http://www.mediafonds.nl/agenda/week/20131207 for an example how the module is used.
FullCalendar.js looks like a good candidate.
Closing, due to age and status of mod calendar