I have stopped maintaing this but I'll leave it available here for anyone still using it.
A lot of the features in this repo have been made redundant by upgrades to nvim win API, and with plugins like nui.nvim now available I don't see a need to maintain this.
If you are looking for a starting point to implement your own custom UI features I would check out these projects instead:
uses non native borders popup.nvim
Floating win API using native borders nui.nvim