Add typography base styles to Astro

The goal is to have this page updated with any changes which was made to the base styles for the redesign.

For example, if we're changing the font-weight and line-heights of h1 tags then it should be reflected here. This would affect all sites which utilize Astro.

@mkokabi If you are making changes to a base style, please share it here. For example, you mentioned that we are updating the appearances of links.