Doc: Update CSS for better dark mode rendering

[titom73]

Change Summary

Update mkdocs theme to be more readable

Related Issue(s)

Related to aristanetworks/avd#1337

Component(s) name

Mkdocs

Proposed changes

• Update link rendering to be more visible
  • Color code for brighter blue in dark mode: #75aaf8 instead of #27569B for light mode
  • Implement a:hover rendering
• Update fonts and font size
• Add better logo for light/dark switcher
• Increase font size for title h4 to h6

How to test

In your development stack:

$ make start

# Wait for mkdocs to come up
# Open http://127.0.0.1:8001

Checklist

User Checklist

• N/A

Repository Checklist

• My code has been rebased from devel before I start
• I have read the CONTRIBUTING document.
• My change requires a change to the documentation and documentation have been updated accordingly.
• I have updated molecule CI testing accordingly. (check the box if not applicable)