title: Add class to div when user scroll down
body: <p>i need to Add class to div when user scroll down, this is my code:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>$(window).scroll(function() { 
     $("#skin_h").removeClass("skin");
     var scroll = $(window).scrollTop();
     if (scroll &lt;= 75) {
        $("#skin_h").addClass("skin_srolld");
     }
  });</code></pre>
  <pre class="snippet-code-css lang-css prettyprint-override"><code>.skin {
      position: fixed;
      z-index: 0;
      top: 0px;
      left: 50%;
  }
  
  
  .skin_srolld {
      top:500px!important;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class="skin" id="skin_h"&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>its not work some help with this please.</p>