Не отображаются стрелки у слайдера

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<link rel="stylesheet" href="https://bootstraptema.ru/snippets/slider/2016/flexslider/flexslider.css"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
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<script>
$(window).load(function() {
 $('.flexslider').flexslider({
 animation: "slide",
 controlNav: "thumbnails"
 });
});
</script>
 
<div class="container">
 <div class="row">
 <div class="col-md-12">
 
 <div class="flexslider">
 <ul class="slides">
 <li data-thumb="http://drawings-girls.ucoz.net/2016/11/rijevolosaya-devushka-s-magicheskimi-sharami.jpg">
 <img src="http://drawings-girls.ucoz.net/2016/11/rijevolosaya-devushka-s-magicheskimi-sharami.jpg" />
 </li>
 <li data-thumb="http://drawings-girls.ucoz.net/2016/11/anime-devushka-so-svetlim-toporom.jpg">
 <img src="http://drawings-girls.ucoz.net/2016/11/anime-devushka-so-svetlim-toporom.jpg" />
 </li>
 <li data-thumb="http://drawings-girls.ucoz.net/2016/11/devushka-s-raspushennimi-volosami.jpg">
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 </li>
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 <img src="http://drawings-girls.ucoz.net/2016/11/devushka-lucefera.jpg" />
 </li>
 </ul>
 </div> 
 
</div><!-- ./col-md-12 -->
</div><!-- ./row -->
</div><!-- ./container -->