Events imported from a mobile phone


I’m new to NextCloud (previously Owncloud 8.2.9) and even newer to the idea of sychronising events.

In my mobile phone (Samsung Galaxy S5) I installed DAVdroid which synchronizes my NextCloud calendar with my default calendar app in the phone (both ways). Everything works fine but… All entries from the phone become transparent (opacity: 0.5) in the NextCloud calendar, which looks awful, like a broken entry.

How can I modify NextCloud to get rid of the opacity feature applied to imported entries?