How to create a GUI for a Python application?

Question

Python

Hello, for a long time I was programming in Python, I mainly wrote utilities and other programs for Linux that do not require a GUI as such, if the interface was then using pseudo-graphics in the terminal. Now there is a need to develop a normal application with a normal beautiful GUI , but bad luck, I don’t know what is best to use for these purposes.
The first thing I started this GTK + Glade with, in Glade and GTK everything is fine, but it is not entirely clear how to implement some things. For example, I want to make dialogs in the application (as in messengers, for example), how to draw all this? What elements from Glade or from GTK to use to display dialogs between users (not buttons of any kind).For good, as I suppose, you need to create some kind of your own component, but how to do this is also not clear, although there are suggestions that you can somehow do this using HTML + CSS.
How can GTK and Glade render everything that I described above correctly?
I'm looking for help from those who are familiar with GUI development with GTK and Python.