• HTML: https://validator.w3.org/
• CSS: https://jigsaw.w3.org/css-validator/

• Color: http://color.hailpixel.com/
• Bootstrap: http://getbootstrap.com/css/

Interact:

• DOM Tutorial: https://dom-tutorials.appspot.com/static/index.html
• HTML CSS games and quizes: http://codepupil.com/
• CSS Bento game: https://flukeout.github.io/
• HTML Markup Man: http://markup.roppychop.com/

• Cascade order: http://www.w3schools.com/css/css_howto.asp
• Layout and positioning: http://learnlayout.com/toc.html
• FLEX: https://developer.mozilla.org/en-US/docs/Web/CSS/flex
• Float: https://developer.mozilla.org/en-US/docs/Web/CSS/float

Reference

• MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript
• Eloquent Javascript: http://eloquentjavascript.net/
• Javascript FAQ: http://www.javascripter.net/faq/index.htm
• Javascript Info: http://javascript.info/

• Codecademy Projects: https://www.codecademy.com/en/tracks/projects
• Command Line Interface (CLI, sometimes called the terminal)
• SS64: http://ss64.com/
• CLI Crash Course: http://cli.learncodethehardway.org/book/