Best learning resource for HTML5/CSS3 for a programmer?

Best learning resource for HTML5/CSS3 for a programmer?

I was just wondering what you thought would be the best education material
for HTML5/CSS3 is (not older web technologies) for a guy who is just a
programmer (i.e. mostly C/C++, Java, Pascal, and Python)? Reason I ask, is
because the HTML and CSS syntax mostly confuses me, and there are some
things I just do not understand (e.g. the float styling attribute, I
usually just end up putting that somewhere and hoping it works, if not,
try putting it somewhere else). So I was hoping there was an explicit
guide/tutorial on getting a programmer up to speed on HTML5/CSS3.
Alternatively, if there is no direct answer to that question, then what is
a good learning resource for HTML5/CSS3 and what are the
pitfalls/shortcomings (if any) in the markup language that I/others might
encounter on this journey/transition?
Keep in mind I have minimal experience writing HTML/CSS markup, and have
written no HTML5/CSS3 markup at all.
Regards and thank you in advance. :-)