doc(anta): Update CSS for better titles readability

[titom73]

Description

Update CSS to make H3,H4,H5 and H6 title bit more readable with more emphasis

To test:

mkdocs serve

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have run pre-commit for code linting and typing (pre-commit run)
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes (tox -e testenv)

[gmuloc]

1. Can we avoid to capitalize code like pipx?
   

2. There is not much difference between Tests Inputs and Input model which makes it look like they are on the same level - is there a way to play with something in CSS?

[titom73]

1. Can we avoid to capitalize code like pipx?
   
2. There is not much difference between Tests Inputs and Input model which makes it look like they are on the same level - is there a way to play with something in CSS?

Last push should have fixed your comments