Where can I find all HTML's and CSS's syntax?

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An HTML5 reference document can be found here:

HTML5 Reference

One for CSS3 can be found here:

CSS reference

Authoritative standards for either mostly don’t exist, as HTML / CSS is not one thing implemented in one place, but rather implemented completely separately in every client that consumes them. The best you can do are guidelines. You won’t find one document that will tell you how to do it ‘perfectly’.