Filing this wonderful resource for the next time I introduce students to the subject.
As an overview, HTML is a hyper text markup language created to give content structure and meaning. CSS, also known as cascading style sheets, is a presentation language created to give content style and appearance.
To put this into laymen terms, HTML determines the structure and meaning of content on a web page while CSS determines the style and appearance of this content. The two languages are independent of one another. CSS should not reside within an HTML document and vice versa.