[www] new layout

Some minor suggestions:

* I miss a different color for visited links.

* most pages uses open sans font. but there are exceptions like https://lists.postgresql.org/ witch uses helvetica. (In general I would prefer web browser font defaults. browser font defaults are the best choice for people with disabilities like dyslexia, …) 

* limit length of a line with max 90 chars (but do not limit mono space lines, avoid line breaking in source code examples.) 

* documentation didn't change. Font size is very small ( 76%), please  get rid of the #EC5800 font color.

* use a light background color to limit brightness ratio.

* Line high could be smaller then 1.8rem, the difference to paragraphs is too small. (I prefer 1.33 -1.5rem)

* top and bottom padding in tables could be smaller