Fix select styles

[Pytal]

Ensure that the styles are always applied correctly

Before	After

The "Before" image shows the share select in https://github.com/nextcloud/server master after opening a file in viewer

[JuliaKirschenheuter]

should we use !important in all places? I can for possible other solution

[raimund-schluessler]

should we use !important in all places? I can for possible other solution

Ideally, we should not use it at all. I know it's sometimes necessary, or rather easier, but I would prefer to limit its usage to the places where we have issues.

[skjnldsv]

should we use !important in all places? I can for possible other solution

Ideally, we should not use it at all. I know it's sometimes necessary, or rather easier, but I would prefer to limit its usage to the places where we have issues.

We could be using a scoped styling with vdeep. It should have a higher selector level?

[susnux]

I agree !important should be used rarely, but for the moment I can only think of one possible "bigger" issue with this:
The enforcement of the primary color on the border, as this makes it hard to assign an error state for custom validation of NcSelect.