W3Schools is the go-to website to start learning any programming language. It's used in college campuses.
CodecademyAnother great resource to learn HTML and CSS.
HTML.comTouted as an easy way for beginners to learn HTML and CSS.
Learn HTML CSSA website with an IDE built in, and all code changes are instantly seen, so you get the feedback you need to build your website.
Mozilla MDNAn incredibly in-depth website, this is the single website that has every tiny detail to create webpages and style them with CSS.