Integrating Python back-end with HTML/CSS/JS User Interface for desktop applications?
Yes you can. You need to choose framework of python. like Django etc. Then you can make own desktop application as you can.
How could I or would it be appropriate to integrate Python code with HTML/CSS/JS as the user interface in creating desktop applications. A simple example; if I wanted to created a function with Python that prints "Hello World!" and use HTML/CSS/JS to create a user interface (make it fancy, perhaps add some images), so I can use it as a desktop application. How would I go about this?
I understand I could use libraries such as Tkinter, but it doesn't allow the flexibility of customising user interface. 
I've read about using Electron, but I haven't seen many people using Python as the back-end. Any help or information in relation to using Python as a back-end with HTML/CSS/JS as the user interface will be greatly appreciated.