As a dark mode resource pack, Volcanic Dark aims to fill the niche of those who want UI that is both pleasing to look at and is actually dark.
This pack also prioritizes visual clarity; You should be able to see what you're doing, after all.
Every feature is confirmed working starting from 1.21.4. Respackopts is supported starting from 1.21
Versions prior to 1.21.2 may be missing some features present in screenshots in the gallery due to older versions of Minecraft simply missing support for later resource pack features. Additionally, colored shulker boxes require either OptiFine or an OptiFine alternative like OptiGUI.
For the sake of transparency, while this is under All Rights Reserved, there are plenty of things you are allowed to do with this resource pack. Note that this list is subject to change in the future. Likely if I find a license that actually has all this stuff included.