We did not create the course geared to a particular certification. However, our web design course is meant to cover modern best practices and introductory technologies including HTML and CSS. Based on that it is likely that taking our course would prepare you well for many web design or web development certifications. Taking a look at that link, it does seem like that is selling a different course. The CodeHS web design and all curriculum is free to use. We do work with different states to make sure the courses get the necessary approvals. Depending on what state you live in there are different requirements.
On the IDE, you can use the CodeHS cloud IDE to write all your code, and that is real valid HTML and CSS. You can always download the code and run locally, but running on the web actually makes it easier for students. Hope that helps!