Workshops
CSS Classes from CSS Conf An introduction to HTML and CSS, with some fancy advanced CSS in the later lessons. Uses interactive examples using CodePen. Has a bunch of challenges and resources near the end.
Codebar’s Tutorials: HTML & CSS An introduction to HTML and CSS, covering the box model and some new HTML elements.
RailsBridge Front-end course An introduction to HTML and CSS, covering some introductory layout techniques and some JavaScript.