[scheduler][styled] Style events based on status

[rita-codes]

Follow up on #18024

• Add styles for the different statuses: accepted, creating, not accepted yet, cancelled, selected accepted, accepted past event, cancelled past event, selected past event. + showing attendees/not showing attendees.
• Include the three variants: regular, compact and all-day events.

[flaviendelangle]

Moving this one to the backlog without a priority since it's fully design