Added snippets for styling elements

A few more snippets. @ebidel, @robdodson PTAL?

Read snippets in the order shown in the README.
Given that we now know that the snippets work without `polyfill-next-selector`, I suggest we don't mention it here. When the docs are updated to show *real* use cases for `polyfill-next-selector`, we can link to the docs. I'll create an issue in this repo for a link to the docs. OK?