Created by: scottaohara
update level 4 headings to level 3 as that would be the expected nesting order after a level 2 heading.
update .excerpt-list__title class to have the same font-size as the h4 selector, to maintain visual consistency.
This commit also contains adding a closing tag for the category posts, as closing s are used for other lists on the site, and this will fix HTML validation errors that are being reported by the browser.