(ON HOLD) CSS Custom Highlight API

[peter-lyons-kehl]

FYI There is a new(ish) "CSS Custom Highlight API". It's stable on Chrome, but not on Firefox yet (for now Firefox has it on Nightly only).

For more: https://github.com/searchmarkers/mark-my-search/issues/144. (For my reference: https://github.com/sapjax/word-hunter/issues/39)

I've subscribed to Firefox updates on that API. Once stable, I'll update here.