This is the beginnings of a "Dark Theme" for the Telegram Web App
I use Stylish to apply this theme in Firefox.
Not too concerned with the structure of this CSS file until I finish tweaking all the different edge cases to my liking (e.g. hover states, select states, special message types)
You can see a diff of the default telegram theme vs the dark theme here.
Or you can just look at the screenshot of the dark theme:
