CSS-only structural child of <simple-shell>. Provides vertical rhythm and prose-friendly max-width.
simple-content is the main article surface. It applies token-correct vertical rhythm (the gap between children uses --a-density-4) and uses prose typography for paragraphs and headings.
Headings cascade naturally. h1 / h2 / h3 receive heading colors via --a-text-heading.
Body paragraphs use a prose line-height (--a-line-height-prose) for comfortable reading.