https://digital.com/tools/html-cheatsheet/
This website provides a bizzare but fascinating cheat sheet for html tags.
https://htmlcolorcodes.com/
An extremely handy color picker for directly converting your choice into an HTML color code.
https://www.codecademy.com/
One of the best learning websites I've ever used for getting a good grasp of the basics.
https://www.w3schools.com/tags/default.asp
Great website with an absolute ton of explanations/tags/tutorials.
Youtube: HTML Crash Course For Absolute Beginners
Crash course Youtube video for HTML that is purported to be one of the best.
Youtube: CSS Crash Course For Absolute Beginners
Another Youtube crash course for CSS from the same creator.
https://www.freecodecamp.org/learn/responsive-web-design/basic-html-and-html5/
Great free intro to HTML.
https://frontendmasters.com/bootcamp/?utm_source=css-tricks&utm_medium=website&utm_campaign=css-tricks-blog-post
A bootcamp for HTML, more of a guided experience. Does require registration, but otherwise free.
https://www.learn-html.org/en/Welcome
Easy to navigate quick links for finding exactly what you need. Also has many other languages in the exact same format.
http://html5doctor.com/element-index/#
Specifically I like htmldoctors element index. Rather than textbook definitions, they give more practical explanations.