Style Overview: include new style features and more CSS info

[annezazu]

Issue Description

Update the styles overview to include copy/paste styles (pulled from here), apply globally (pulled from here), and more info around custom CSS usage (specifically pulling in feedback from here WordPress/gutenberg#49415 (comment))

URL of the Page with the Issue

https://wordpress.org/documentation/article/styles-overview/

Why is this a problem?

We want to set folks up for success with this lesser known features so it makes sense to cross include some of the tooling and provide more context around CSS.

@kathrynwp in case you might be able to help!

[zzap]

Heads up @WordPress/docs-issues-coordinators, we have a new issue open. Time to use 'em labels.

[mrfoxtalbot]

Thank you! Cc'ing @kathrynwp as she's been working on this too.