add osx guide to run website locally

Signed-off-by: Sven Nierlein <sven@nierlein.de>
removed duplicate affix code

there is no need to have this code twice.

Signed-off-by: Sven Nierlein <sven@nierlein.de>
removed duplicate css and layouts

instead of duplicating a layout file just to change 1 line, we
can use variables and conditionals to make layout better maintainable.

Signed-off-by: Sven Nierlein <sven@nierlein.de>