th.rotate-text {
  vertical-align: bottom;
  text-align: center;
  width:35px;
}

  th.rotate-text span {
    -ms-writing-mode: tb-rl;
    -webkit-writing-mode: vertical-rl;
    writing-mode: vertical-rl;
    transform: rotate(180deg);
    white-space: nowrap;
  }