MDN HTML
The HTML reference section contains links to tutorials, an element reference section, and basic information. This resource page would be helpful for those who are beginning to code as an information source. It is also helpful for grabbing bits of code from the reference section to try in your own coding. I like resources like these so I can compare how different attributes will affect my code.
MDN CSS
The CSS reference page is a huge set of resources. It includes tutorials, reference section, a cookbook, and links to demos. It is a great site for those beginning to learn styling.The cook book has a set of ideas on how to style different elements. It uses a recipe format and allows you to grab bit of code as well as showing an example of how the code will look in a final product.
Conclusion
Resource materials such ase these are imperitive for any developer. With today's technology, things are changing so quickly that it would be nearly impossible to know all the code all the time. When new pieces of code come out or new ways of problem solving code it is nice to have a trusted resource to show the most up to date ways of coding a particular element on a page and how to style it properly.