When creating an event, there are 4 different tabs: Summary, Recurrence, Participants, Attachments. It is not distinct enough which tab is the opened one.

Steps to reproduce:

1. Create an event
2. Click on the tab "participants"

Actual results:
when clicking on the title "participants" and thus, opening the tab, it is visible by being written in a new colour (black). But the distinction from the other (closed) tabs is not distinct enough.

Expected results:
To make sure that the user can see on the first view which tab is opened, it would be better to make the not opened tabs less distracting by putting them in the background. Therefore, the background of these tab titles could by grey as well as the delimiting line could be thicker and thus more marking off.