til / Rotate in CSS with turn
There are several ways1 to rotate items using CSS. The most common is using degrees (deg), to describe rotations from 0 to 360. Another option is radians (rad), which uses values from 0 to 2π. But, a more intuitive approach that doesn’t involve math terms is to use turns (turn).2
  0.25
0.25turn / 90deg / 0.5708rad
  0.5
0.5turn / 180deg / 3.1416rad
  -0.125
-0.125turn / -45deg / -0.7854radEven though I was unaware of this until yesterday, browser support is great,3 even IE 9 supports it.