Matches nav bar and post page fallback styles to react component styles

[cindywu]

This PR updates the styles for the fallback of search in nav bar and post content in editor. Prior to this PR the fallback styles did not match the styles of react components producing a clunky user experience when loading the page.

• [x] add 1em padding-bottom for p without .Prosemirror
• [x] add 1em padding-bottom h2, h3, h4 without .Prosemirror
• [x] add 1em padding below blockquote
• [x] fix search-fallback styles to match react component for search in nav

before: left = fallback, right = react components rendered

after: left = fallback, right = react components rendered

[linear[bot]]

JEL-226 Match editor preview styles with editor component styles (spacing between paragraphs)

* [X] add 1em padding-bottom for `p` without `.Prosemirror` * [X] add 1em padding-bottom `h2, h3, h4` without `.Prosemirror` * [X] add 1em padding below `blockquote` * [X] fix `search-fallback` styles to match react component for search in nav add spacing between paragraphs in preview render of post before editor renders