Nice and dark, with a slow smooth animation rather than fast, bright, and jarring. This theme gets it. Just because it allows animation, it doesn't need to be "HELLO! CHECK OUT MY ANIMATION! IT'S HERE!!!". The infinity symbol is a pleasing color that pairs well with the black background and it's animation is subtle, not distracting you from the content you're reading/watching.

I would give five stars, but I'm not a huge fan of the color chosen for the text on the active tab or the bookmarks on the bookmark toolbar. I would've probably switched the white and cyan around for active and inactive.