Tài liệu Customizing the Main SECTION Element

Two ARTICLE elements are placed within the SECTION
element.
The id attribute for both ARTICLE elements is unique
to allow you to easily identify which element is which. Instead
of linking to an external CSS class, a style attribute is used for
both ARTICLE elements. The style attribute is using CSS, but it
is localized to that single element and is not shared with other
elements.
Each ARTICLE element also contains H1 and P elements.
The H1 element is a header that will be used to lead in each
article title. The P element is a paragraph element for content.
Placeholder text is added to the H1 and P tags so you can see
where the content
is when you view the page in an HTML5-
compliant web browser.
The final HR element is a visual separator between the two
ARTICLE elements