Client: [macOS] [Mojave] No boxes surrounding the settings sections anymore

[ChrisEdS]

The former client (<= 2.5.0) had gray boxes around the different sections. This increased the user experience. It seems as if there is a regression here.

---

Expected behaviour

Actual behaviour

Steps to reproduce

1. Install 2.5.1 daily build
2. Go to General or Network tab

Client configuration

Client version:
2.5.x
Operating system:
macOS Mojave
OS language:
English
Qt version used by client package (Linux only, see also Settings dialog):
Qt 5.10.1 - ownCloud-2.5.1.10736-daily20181022

@guruz @ogoffart

[ogoffart]

The box are still there, for me on linux.
I think that's the style on macOS Mojave

[ogoffart]

But maybe the boxes are gone because that's how mojave's style is.
I mean, maybe the box disappeared from every application.

[ChrisEdS]

Same system different style:

Left: 2.4.3 client from customer.owncloud.com portal | Right: 2.5.1 client from ownCloud

[michaelstingl]

Boxes come back with Qt 5.12.1:

Thanks @dschmidt for building it!

[guruz]

So.. do we want 5.12.1 with 2.5.3?
This would also help with https://github.com/owncloud/client/issues/6968

[guruz]

Boxes are back according to comment above and according to https://github.com/owncloud/enterprise/issues/3138#issuecomment-465055091

See discussion regarding dark mode in https://github.com/owncloud/client/issues/7043#issuecomment-465448121