Personally, I find that out of the 9 of the hundred that was mentioned in this article from fast co design dot com, the most important design idea was the concept of Net Art. I view net art as it being concentrated on exploring the breadth that HTML and CSS could encompass, therefore net art is the foundation of creating new layouts and design for the web. Originally, net artists are more concentrated with trying to break down the customs of traditional art. This has started the movement of utilizing coding to create an "unconventional" medium of work. Sort of like what punk is to rock n roll.
To reiterate, net art is the barebones of transforming the internet in my opinion (apart from the obvious binary and infrastructure ****), which makes it a very important facet of the concept of digital art and design. It promotes the usage of creating a "digital renaissance" for the internet, including revolutionizing the visual aspects in our daily lives in the digital realm.
wwwwwwwww.jodi.org and http://yyyyyyy.info are prime examples of how net art has revolutionized thinking about the capacities of what HTML and CSS could offer. Although I think that both of these websites are thought experiments, these sites have also helped advance the limits of what HTML and CSS could do by allowing the user to interact and explore the content of which it has to offer, creating a space where art can mingle with play.