Use tabs consistently.
Rename pics folder to img.
Move back.png in img folder.
site.css: remove units from zero.
site.css: make it more readable.
site.css: remove inherited font property.
html:

* specify a doctype
* specify lang
* specify meta charset
* remove type for css and js files
* add alt tag for img
index.html:

Fix validation errors and reindent for better readability.
Move google font in the html to enable parallel downloading.