Semantic UI – Search Selection not working

I’m trying to use the Semantic UI – Search Selection, but it’s not working.

I got the code from their website (here) but it does nothing…

Code:

<div class="ui fluid search selection dropdown">
  <input type="hidden" name="country">
  <i class="dropdown icon"></i>
  <div class="default text">Select Country</div>
  <div class="menu">
    <div class="item" data-value="ad"><i class="ad flag"></i>Andorra</div>
    <div class="item" data-value="ae"><i class="ae flag"></i>United Arab Emirates</div>
  </div>
</div>

Even if I initialize it on jQuery it doesn’t work:

jQuery('.ui.dropdown')
  .dropdown()
;

What am I doing wrong?
Is there something else I need to do to make it to work on WordPress?