This is a basic article layout used for creating the header images that go at the top of articles.
I've set up the basic HTML and CSS, but if you prefer to use Sass for your CSS, that's fine also. Place the HTML for your demo in the index.html file where marked, and style it using the custom.css file.
Articles themselves are written using Markdown. See the posts here here for reference. I've put together a writing guide for writing the article too.