Summary

When using Atlassian's Team Calendars and RefinedSpaces' theme with image background, the calendar is transparent (see screenshot).

Replication Steps:

1. Install RefinedSpaces
2. Go to a space's settings/Look and Feel and select RefinedSpaces for themes.
3. Add the Team Calendar add-on
4. On a space, add a calendar (or add a Team Calendar macro to a page)
5. When the calendar has been saved, go to the Calendar-part of the Space