.trigger {
   background-image: url("images/collapse-icon.png");
   cursor: pointer;
   float: right;
   height: 17px;
   margin: -22px 8px 0 0;
   position: relative;
   width: 9px;
   z-index: 1;
}

.active {
   background-position: left top;
}
.inactive {
   background-position: left bottom;
}