Custom nub arrow

_nubbed.scss

div.nub {
    border-bottom: 16px solid rgb(250,250,250);
    border-left: 16px solid transparent;
    border-right: 16px solid transparent;
    content: '';
    height: 0;
    margin-left: -16px;
    position: absolute;
    top: -16px;
    width: 0;

    &:before {
      border-bottom: 17px solid $base-border-color;
      border-left: 17px solid transparent;
      border-right: 17px solid transparent;
      margin-left: -17px;
      position: absolute;
      top: -17px;
    }
  }