unitless line-height
replace px values by em (where trivially possible)
create font size variables
replace font sizes by % values and keywords
fix sectionpage flags
fix search height
scale logo
header nav block element
stop instance settings navigation from scrolling

we cannot know the top offset
revert feedback font-size to 12px
revert morelink font-size to 0.8em
Merge pull request #685 from xi/feature-480-font-size-2

flexible font size