config: config CSS rework

[Rakibei]

Reworked a large part of the CSS for the Cactbot config.

The goal was to make it easier for the user to get an overview of the different configs sections.
Has the added benefit of adding a distinction between the different sections, as mentioned in issue #1120.

The pull request is technically ready but I would like hear some feedback so I am leaving it as a draft for now.

[xiashtra]

My first reaction is that there is way too much padding between the elements.

[valarnin]

I agree with xiashtra, the amount of added padding here is going to significantly increase the scrolling required on an already massive page.

In addition, I just want to confirm - this was tested in OverlayPlugin's Cactbot Config tab, correct? I see several new CSS properties in use, and while a quick spot check didn't show any issues, OverlayPlugin's CEF/Chromium version is still at v95, which might cause compatibility issues.

(I like the overall change in look and feel here, FWIW)

[Rakibei]

I made the padding as small as I could without it looking weird, so now it is pretty much as close to the old version as possible.

And yeah I've tested it on the OverlayPlugin's inbuilt Cactbot Config tab

@valarnin so if this looks fine then I'll turn this into a normal PR