Very cool. The editor has live preview, syntax autocomplete, colour pickers, and different colour themes to choose from.
Can even use it to customise it's own UI, nice!

Brilliant, allows me to customize my most visited sites exactly how I want. Most of all it lets me live in my world of Dracula.

Used Stylish for ages, don't know why I didn't switch sooner. Besides not having the shady past of it's older counterpart, the coding environment is so much nicer, live preview, syntax autocomplete, colour pickers, customisable UI/UX.