cssText should be text (not bytes)

[jaraco]

In this line, I found I had to decode the cssText in order to print it, a legacy behavior. Let's figure out how to represent text naturally and encode only when necessary.

[jaraco]

This change may be backward incompatible, and if that's the case, let's be sure to provide detailed migration guidance. We may even want to consider having a deprecation period with the current behavior and a way to opt-in to the future behavior before making it the default behavior. That can only work if providing both interfaces side-by-side (similar to how Python 2 handled bytes and str interchangeably).

Let's start by just switching from bytes to text and providing guidance on how to migrate and see how onerous the migration appears.