.zambezi-grid-header.is-sort-ascending,
.zambezi-grid-header.is-sort-descending {
  background-color: #BBB;
  box-shadow:
    inset 0 1px 0 yellow
  , inset 0 2px 0 black
  ;
  padding-right: 16px;
}

.zambezi-grid-header.is-sort-ascending:after,
.zambezi-grid-header.is-sort-descending:after
{
  content: "↑";
  position: absolute;
  top: 5px;
  right: 5px;
  display: block;

}

.zambezi-grid-header.is-sortable {
  cursor: pointer;
}

.zambezi-grid-header.is-sortable:hover {
  background-color: yellow;
}

.zambezi-grid-header.is-sort-descending:after
{
  content: "↓";
}