

  div
    {
      background-color: green;
      border-left: green solid 35px;
      border-right: green solid 15px;
      height: 100px;
      left: auto;
      position: absolute;
      right: 80%;
      top: 0px;
      width: 50px;
      writing-mode: vertical-lr;
    }

  /*
  "
  4. [If] 'left' is 'auto', 'width' and 'right' are not 'auto', then solve for 'left'
  "
  10.3.7 Absolutely positioned, non-replaced elements
  http://www.w3.org/TR/CSS21/visudet.html#abs-non-replaced-width

  So:

        