I added a style sheet to esp32-manager using Milligram. Milligram is a minimalist CSS framework that features styling for many web elements such as buttons, fields, forms and more. And it only weights 3kB when compressed, ideal for a device as tiny as the ESP32!
This was what the old interface looked like in plain HTML
This is what it looks like now using Milligram
The project is hosted in GitHub. Check it out: https://github.com/pablobacho/esp32-manager