Monal controls doesn't follow MacOS theme

[roman901]

Description of my issue or feature request:

Follow to #683 - other parts of UI doesn't follow a system UI theme

System information (if you can provide):

macOS Monal & system version: Monal 5.0 Alpha / Big Sur

Additional information like screenshots:

If you can reproduce your issue: send us your log file (Settings/Log) to info (at) monal (dot) im. PLEASE BE AWARE THAT THIS CAN PROVIDE SENSITIVE INFORMATION TO THE DEVELOPERS (which of course will not abuse this, but you are informed now!)

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[ ] I have cross-checked this overview https://github.com/monal-im/Monal/issues/322 as well as filtered for related labels https://github.com/anurodhp/Monal/labels [ ] I have checked that at least XEP-198, XEP-0280, XEP-0352, XEP-0357 and XEP-0163 are activated on my server and shown as 'green' under Settings-->Account-->(i) in server column (under advanced settings) [ ] I have checked that all checkboxes are ticked under Settings --> Notifications