Hi,

Yes with Odoo 9.0 you are able to develop websites and all kind of views using HTML5 and CSS3, better than that bootstrap integration and awesome fonts are by default supported.

But in anyway, you will not recognise a fully static HTML in odoo modules, but instead of that a templating engine is available by default in Odoo and it's called Qweb...you can read more about it in documentations :

https://www.odoo.com/documentation/9.0/reference/qweb.html

Good luck,

Yes , Odoo Full support html5 and Css3 you can write any HTML code in xml file and the framework will run it Successfully