The default light-grey backgrounds used for containers along with the irregular rounded corners never really spoke to me.
So I fixed that.
Mintcraft is a resource pack I made mostly to fit my own needs and tastes, but has proven to be liked by at least 3 other beings of human nature within this galaxy.
Taking some inspiration from the Minecraft Launcher's giant PLAY button, Mintcraft aims to provide a consistent dark mode and slightly refreshed look to the Minecraft UI.
Stress being on UI: This pack mainly affects the solid backgrounds of the options and world/server selection screens, as well as various buttons and containers in-game. If you'd like, you can also apply my take at the Minecraft Seven font, Mintbit, and a new button click sound via add-ons. Or download the Complete version to get all of that in one handy ZIP.