To style the <h2> specifically, a descendant selector is used. It sets the size, weight, color, padding and margin as well as border-bottom.
Up till now, the <h2> element has had a margin on top of the element, which has been creating a gap between the the header container and the left and right containers. Now that the margin has been removed from the <h2> element (using "margin: 0"), this gap disappears.
div#content h2articles and presentations