extract `.contents`-related styles to a `content.less`
iterate on style.
more iteration.
add more.
add avenir font
optimize background image.
on topic page, make 'time' a link
stress that we can add styles for paragraph tags.
style list items a bit more.
housekeeping: this style and comment are meaningless. remove them.
Merge branch 'dec-15-style' into 'master'