Calendar app, color picker not working with Safari

[RetroYogi]

Expected behaviour

In the calendar app, when selecting the "..." menu next to a calendar, then choosing "edit color", it opens a color picker (the one from the web browser) which allows to pick a color for that calendar.

Actual behaviour

In Safari on macOS, the color picker opens but disappears again as soon as the mouse cursor moves. This makes it impossible to pick a new color.

Steps to reproduce

1. With the Safari browser on macOS, select the calendar app
2. click on the "..." next to a calendar's name
3. click on "edit color"
4. click on the color itself
5. mouve the mouse

Client configuration

Initially encountered bug with macOS Big Sur and Safari 14.1 - Intel MacBook Reproduced bug with macOS Catalina and Safari 14.0 - Intel Macmini

Server configuration

Initially encountered bug on with Nextcloud 21.0.1 (self hosted) Reproduced bug with a free Nextcloud account on woelkli.com, version unknown

https://user-images.githubusercontent.com/60404287/117166611-d2ff2b00-adc6-11eb-9498-fb82356bc13d.mp4

[raffisweb]

Color Picker is usable if you first click something on the page and then try opening the ... menu. Might be a layer-issue.

https://github.com/nextcloud/calendar/issues/4508#issuecomment-1245893303