.simple-tree-table-icon {
  display: inline-block;
  width: 1.5em;
  line-height: 1.5em;
  margin: 0.1em;
  background-color: #eee;
  text-align: center;
  cursor: pointer;
}
.simple-tree-table-opened .simple-tree-table-icon:after {
  content: "-";
}
.simple-tree-table-closed .simple-tree-table-icon:after {
  content: "+";
}