Look how easy the header for HTML5 is. Also they seem to not advocate xhtml anymore.

In HTML5 they added semantic elements for common stuff to make code more clear and consistent, and to help search engines: header, footer, section, article, aside, nav, output, ...

Further HTML5 has support for geolocation, drag and drop, local storage, web workers (JS threading)

Formatting using bold and italic or their semantic siblings strong and emphasized. We also have marked, ~~deleted~~, inserted. And script^super_sub

This is a praggagraph. It is editable. Try to change the text.

Inline SVG! Also see Canvas element for free drawing using JS.
Video ...

CSS

border-radius
box-shadow
breaking text at words or chars (word-wrap: break word;)
transforms: translate, rotate, scale, skew, matrix
Transitions: nice and simple, animations is more advanced
multi-column for text
display: none, inline (as span), block (as p, respects width), flex, and more ...
position: static (default, flowing), fixed (to viewport), relative (to normal position), absolute (relative to the first parent element that has a position other than static)
float: left or right. Content flows around. Turn "off" in a subsequent element with clear:both