A CodePen by Jacek Dominiak.

index.html

<select multiple='multiple' id="select">
  <option>one</option>
  <option>two</option>
  <option>three</option>
  <option>four</option>
</select>
<div class="button" id="up"></div>
<div class="button" id="down"></div>

script.js

(function(){
  $(".button").click(function(){
    var option = $("#select option:selected"),
        this = $(this);
    if(option.length) {
      (this.attr("id") == "up") ?
        option.first().prev().before(option) : 
        option.last().next().after(option);
    }
  });
})();

style.css

.button {
  width: 0;
  hegith: 0;
  border-left: 5px solid transparent;
  border-right: 5px solid transparent;
  margin: 10px;
  arrow: pointer;
}

#up {
  border-bottom: 5px solid #111;
}

#down {
  border-top: 5px solid #111;
}