A call for source code CSS

It sounds like an editor that works in abstract syntax trees and writes out screen (styled) and disk (pep 8) representations.

That is a good idea! One difference from CSS though is that code presentation rules should be reversible. E.g. when you author a Python code with more than 79 characters in line, your environment should seamlessly convert it to PEP-8 compliant source before checking it into the repository.