style.css

/* Core Styles */

* {
  box-sizing: inherit;
}

.combobox {
  display: inline-block;
  position: relative;
  box-sizing: border-box;
}

.combobox input {
  margin: 0;
}

.combobox .open {
  background: #eee;
  border: 1px solid #ccc;
  border-left: none;
  font-size: 0;
  height: 24px;
  width: 24px;
  line-height: 24px;
  padding: 0 3px;
  display: inline-block;
  text-align: center;
}

.open.disabled {
  color: #ccc;
}

.combobox .open:before {
  content: '\25BE';
  font-size: 12px;
}

.combobox .options {
  position: absolute;
  top: 100%;
  z-index: 9999;
  min-width: 100%;
  padding: 0;
  margin: -1px 0 0;
  border: 1px solid #ccc;
  background: #fff;
  list-style-type: none;
  max-height: 240px;
  overflow: auto;
}

.combobox .options.flip {
  top: auto;
  bottom: 100%;
}

.combobox .options .option {
  border-bottom: 1px solid #eee;
  margin: 0;
  padding: 3px 6px;
  cursor: default;
}

.combobox .options .option:hover, .combobox .options .option.hilighted {
  background-color: #f5f5f5;
}

.combobox .options .option:last-child {
  border-bottom: none;
}