Implement spacings and font styles for desktop and mobile

[obulat]

Fixes

Fixes #215 by @panchovm
Fixes #220 by @panchovm

Description

This PR adjust the site's layout (margins, padding, font sizes, etc) to match v2 of the designs both for desktop and for mobile.

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the default branch of the repository (main or master).
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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