This website offers a wide variety of learning resources and sections on HTML and CSS with each individual option listed on the side along with samples and areas where you can experiment with what they are teaching.
The MDN website has a lot of free tutorials for HTML and CSS as well as alot of other resources on coding. They also have a "Play" link at the top so you can practice any new skills you've learned.
This is the Free Code Camp YouTube channel that offers alot of video tutorials that are worth perusing to learn about HTML and CSS and other topics. One drawback is you can't search a page for one specific thing you are looking for when in a pinch.
This is an open source site that offers turorials on different subject matters. They offer "High quality coding education maintained by an open source community."
This website was developed by Google and offers courses for different topics including HTML and CSS. The information provided offers the most up to date best practices and links to other resources.