<div class="grid">

  <div class="item">
    <div class="item-content">
      <!-- Safe zone, enter your custom markup -->
      This can be anything.
      <!-- Safe zone ends -->
    </div>
  </div>

  <div class="item">
    <div class="item-content">
      <!-- Safe zone, enter your custom markup -->
      <div class="my-custom-content">
        Yippee!
      </div>
      <!-- Safe zone ends -->
    </div>
  </div>

</div>

<script src="https://cdnjs.cloudflare.com/ajax/libs/web-animations/2.3.2/web-animations.min.js"></script>
<script src="https://cdn.jsdelivr.net/gh/haltu/muuri@0.9.5/dist/muuri.min.js"></script>

.grid {
  position: relative;
}
.item {
  display: block;
  position: absolute;
  width: 100px;
  height: 100px;
  margin: 5px;
  z-index: 1;
  background: #000;
  color: #fff;
}
.item.muuri-item-dragging {
  z-index: 3;
}
.item.muuri-item-releasing {
  z-index: 2;
}
.item.muuri-item-hidden {
  z-index: 0;
}
.item-content {
  position: relative;
  width: 100%;
  height: 100%;
}

var grid = new Muuri('.grid');

// To make the items draggable
// try this next...
// var grid = new Muuri('.grid', {dragEnabled: true});