<div id="wrap">

    <!-- section -->
    <div class="section">
      <div class="center">

        <h3>Scroll</h3>

        <div id="scroll">
          <div class="scroll">

            <div class="scrolled">
              <span>We scrolling!</span>
            </div>
            <div class="scrolled">
              <span>We scrolling!</span>
            </div>
            <div class="scrolled">
              <span>We scrolling!</span>
            </div>
            <div class="scrolled">
              <span>We scrolling!</span>
            </div>
            <div class="scrolled">
              <span>We scrolling!</span>
            </div>
            <div class="scrolled">
              <span>We scrolling!</span>
            </div>
            <div class="scrolled">
              <span>We scrolling!</span>
            </div>
            <div class="scrolled">
              <span>We scrolling!</span>
            </div>
            <div class="scrolled">
              <span>We scrolling!</span>
            </div>
            <div class="scrolled">
              <span>We scrolling!</span>
            </div>
            <div class="scrolled">
              <span>We scrolling!</span>
            </div>
            <div class="scrolled">
              <span>We scrolling!</span>
            </div>
            <div class="scrolled" id="fixed">
              <span>This is fixed!</span>
            </div>
          </div>

        </div>

      </div>
    </div>
    <!--/section -->

  </div>

html,
body {
  margin: 0;
  padding: 0;
  font-family: sans-serif;
  font-size: 16px;
  line-height: 1.4;
  color: #555;
  background: #fff;
}

* {
  box-sizing: border-box;
}

#wrap {
  position: relative;
}

.section {
  padding: 40px 20px;
  border-bottom: 1px solid #ddd;
  
  &:last-child {
    border-bottom: 0;
  }
}

.center {
  width: 100%;
  max-width: 980px;
  margin: auto;
}

h3 {
  margin: 0 0 32px;
  font-size: 24px;
}

/* SCROLL */

#scroll {
  width: 280px;
  height: 280px;
  margin: auto;
  box-shadow: 0 0 0 1px #aaa;
  position: relative;
}

.mCSB_inside > .mCSB_container {
  margin-right: 0;
}

.scroll {
  width: 100%;
  height: 100%;
}

.scrolled {
  padding: 10px;
  text-align: center;
  
  &#fixed {
    background: #777;
    color: #fff;
    position: absolute;
    z-index: 1;
    top: 0;
    left: 0;
    width: 100%;
  }
}

$(function () {

  function treatScroller($scrolledContainer, $fixedItem) {
    $scrolledContainer.css({
      paddingBottom: $fixedItem.innerHeight()
    });
  }
  
  function treatFixed($fixedItem, $container, $scrolledContainer, top) {
    var fixedItemHeight = $fixedItem.innerHeight(),
      containerHeight = $container.height()
    
    $fixedItem.css({
      top: containerHeight - top,
      marginTop: fixedItemHeight * -1
    });
  }

  $('.scroll').mCustomScrollbar({
    theme: 'dark',
    scrollInertia: 200,
    callbacks: {
      onInit: function () {
        treatScroller($('#' + this.mcs.content.attr('id')), $('#fixed'));
        treatFixed($('#fixed'), $(this), $('#' + this.mcs.content.attr('id')), this.mcs.top);
      },
      whileScrolling: function () {
        treatScroller($('#' + this.mcs.content.attr('id')), $('#fixed'));
        treatFixed($('#fixed'), $(this), $('#' + this.mcs.content.attr('id')), this.mcs.top);
      }
    }
  });
});