Visitor mastering HTML and CSS was the first step in Web Design and actually the least interesting of the "design" aspect. Next up you learn how to make a Web Layout in Photoshop and convert that mockup to HTML and CSS code to make a functional Web Site.
Essentially this is where you put the whole process together. Are you ready?
First up is Chapter 1: Design the Site. For designers, this should be the fun part.
To complete the Mission work through the tutorial and take a couple screenshots as evidence of what you learned.
Mastery is simple, Visitor. You just need to post what you learned on your SITREP.