Fix calendar CSS

[niccokunzmann]

The CSS of events and calendars needs changing:

.CALENDAR-INDEX-0, .CALENDAR-INDEX-0 .dhx_body, .CALENDAR-INDEX-0 .dhx_title 

will work with day, week, month view.

---

We're using Polar.sh so you can upvote and help fund this issue. We receive the funding once the issue is completed & confirmed by you. Thank you in advance for helping prioritize & fund our work.

[niccokunzmann]

The best thing to make it easy for people styling the calendar here is to set the CSS classes in the sub-elements, too, so we can just use one CSS selector.