The HTML page on MDN is an extensive list of how to program HTML as well as the different elements available and how each should be used. This page offers a variety of tutorials on how to use HTML to create tables, forms, embedded media, and basic design. It also goes over more advanced techniques as well.
The HTML Reference area provides information on all HTML elements and attributes. The elements page goes over each element, how it is used, and best usage for it. Each element can be clicked on to get further information on how to use it along with examples of it in use, attributes that go along with it, and accessibility info. These pages also show which browsers this element does and does not work in.
The attribute page looks at the different attributes that can be used with various elements. It shows how they are used and which element it is valid in. Some attributes have their own pages with examples and further information.
The CSS page on MDN contains resources, tutorials, and a full reference of css properties and values. There is introductory information on starting out with CSS and how to use them for styling and layout on a website. There is a full learning area with modules to guide you through learning CSS usage. Additionally, there are guides for major concepts in CSS like flex, grid, box, backgrounds, media queries, and more.
A full list of properties is arranged alphabetically and within each property there are demos of using this property, syntax on how to use it, examples of it in use, and a browser compatibility chart for that property.
Both of these pages offer a wealth of information for anyone that works with web design and coding. There is an extensive list of elements for both HTML and CSS. It’s hard to remember everything when you are learning to code. These pages are a valuable resource to look up how to use a certain element, or to find that specific element that does what you want it to do. I often use resources like this when I don’t know how to do something, or if I can’t remember quite how to use all of the attributes for a certain element.
Having a trusted source for this information is important because HTML and CSS are changing and evolving all the time. New elements arrive and older ones are retired. It’s important to know what the best option to use is when coding because using outdated code can make a page not display as desired.