I agree with the other comments but would stress that there is no reason NOT to start out learning HTML5 and CSS3. They are basically super-sets of their predecessors, plus you will avoid getting into bad habits by using obsolete code.
However, one word of caution: Check the browser support for the new features in HTML5/CSS3. Some are well supported by current browsers, others are not. And IE8 and below support none of them. That is less of a problem as IE8 usage is dying out, (and the impending demise of Windows XP may hasten that), but it should be borne in mind anyway.