Prism Theme (+ Style Settings plug-in)
(Note: Slightly modified Fancy Blockquote css snippet by @EleanorKonik also being used in the above screenshot)
I was a hard-and-fast believer in the base obsidian theme—it was sleek and wonderful. I loved (and still love) the base theme, almost looking down on those who felt the need to change their Obsidian theme. The Prism theme changed all of that for me. As soon as I saw it I fell in love, wasting time I should have been using toward actual work just setting it up and I see no reason to ever go back.