chore: Integrate custom-styles shortcode in the theme

[JTorreG]

Proposed changes

Adds the content of the custom-styles shortcode (used almost everywhere in the docs repo) to the theme. This makes it unnecessary to remember to add the {{}} shortcode to each doc.

The shortcode improves the spacing in some components to make the text more readable.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• I have updated any relevant documentation (README.md and CHANGELOG.md)