AdminLTE is by far one of the great examples of what Bootstrap CSS can do and consists of pre-defined UI elements used for Admin control panels. Similarly we have ElementUI, Bulma, and Bootstrap CSS in its core. 

Right now, there’s a massive amount of various admin panels on the net.

AdminLTE Midnight Theme
AdminLTE Midnight Theme

So, I made a quick Proof of Concept on how we can easily convert default AdminLTE layout into a dark theme, with a bit of help from grunt and yarn.

AdminLTE Midnight Dark Theme is available on GitHub. I added a detailed description on how to run it in dev mode via AdminLTE repository.

You might find it useful to go through customisation instructions first.