Use typing.Optional and typing.Union to be compatible with python3.9 …

[bwesen]

…in styles.py

Description

Fix some minor python3.10-esque typing changes in modules/styles.py so it still works on python3.9 as well

Checklist:

• I have read contributing wiki page
• I have performed a self-review of my own code
• My code follows the style guidelines
• My code passes tests

[bwesen]

Don't know why the warning "Pull requests can't target master branch" is there, as the PR targets the dev branch...

[w-e-w]

this kind of annotations is used all over webui
the way to fix this for old python is to add from __future__ import annotations in at the top

• PEP 604 annotations #15259

I was the one who fogot to add from __future__ import annotations when I was working on styles.py

[AUTOMATIC1111]

closed in favor of the other solution