[Modification request] Allow for headings in Prose component to be more distuinguishable

[seangolob]

The SWP team has received a request to make the headings in the prose component more distinguishable based on the heading level.

Related issue: https://github.com/github/brand-and-marketing-epd/issues/671

Notes from the related issue

Context Could we please adjust the sizing of H3 headers in our Contentful SEO page templates? Currently, depending on the viewport size, the H3 headers appear nearly identical to H2 headers, which can cause confusion and affect the visual hierarchy of our content.

Example only the first heading is a H2 the rest are H3s. URL: https://github.com/resources/articles/security/what-is-a-data-breach

End notes

This will require design feedback first. CC @simmonsjenna @nsolerieu

This may be a no-op but I think we can use this as a point of feedback.

Thanks!