Today, I think I can safely say that I've tweaked it enough to a usable state that I can now share it with the world. Below are some screenshots to show how it looks like in general.
To install it, first, download the theme file from my GitHub.
[sprite-1_elementary_v1.1.tdesktop-theme]
- Click the hamburger menu on the top right of the telegram desktop client.
- Go to Settings > Chat Settings.
- Under the Chat background section, click Choose from file and select the theme file.
- Telegram will ask you if you want to keep the theme, just click the Keep Changes button.
I would love to get some feedback so tell me if something is broken or looks off and I'll look into it.
P.S. If you want the thinner title bars for non-GTK apps too, refer to this page. I update it whenever I find some new tweak for elementary OS.