.rotation-wrapper-outer {
  display: table;
}
.rotation-wrapper-inner {
  padding: 50% 0;
  height: 0;
}
.element-to-rotate {
  display: block;
  transform-origin: top left;
  /* Note: for a CLOCKWISE rotation, use the commented-out
     transform instead of this one. */
  transform: rotate(-90deg) translate(-100%);
  /* transform: rotate(90deg) translate(0, -100%); */
  margin-top: -50%;

  /* Not vital, but possibly a good idea if the element you're rotating contains
     text and you want a single long vertical line of text and the pre-rotation
     width of your element is small enough that the text wraps: */
  white-space: nowrap;
}