- HTML---------------------------------------------------------------------------

<ul class="box">
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
  <li></li>
</ul>


- CSS ---------------------------------------------------------------------------

ul.box {
position: relative;
z-index: 1; /* prevent shadows falling behind containers with backgrounds */
overflow: hidden;
list-style: none;
margin: 0;
padding: 0; }


ul.box li {
position: relative;
float: left;
width: 250px;
height: 150px;
padding: 0;
border: 1px solid #efefef;
margin: 0 30px 30px 0;
background: #fff;
-webkit-box-shadow: 0 1px 4px rgba(0, 0, 0, 0.27), 0 0 40px rgba(0, 0, 0, 0.06) inset;
-moz-box-shadow: 0 1px 4px rgba(0, 0, 0, 0.27), 0 0 40px rgba(0, 0, 0, 0.06) inset; 
box-shadow: 0 1px 4px rgba(0, 0, 0, 0.27), 0 0 40px rgba(0, 0, 0, 0.06) inset; }


ul.box li:before,
ul.box li:after {
content: '';
z-index: -1;
position: absolute;
left: 10px;
bottom: 10px;
width: 70%;
max-width: 300px; /* avoid rotation causing ugly appearance at large container widths */
max-height: 100px;
height: 55%;
-webkit-box-shadow: 0 8px 16px rgba(0, 0, 0, 0.3);
-moz-box-shadow: 0 8px 16px rgba(0, 0, 0, 0.3);
box-shadow: 0 8px 16px rgba(0, 0, 0, 0.3);
-webkit-transform: skew(-15deg) rotate(-6deg);
-moz-transform: skew(-15deg) rotate(-6deg);
-ms-transform: skew(-15deg) rotate(-6deg);
-o-transform: skew(-15deg) rotate(-6deg);
transform: skew(-15deg) rotate(-6deg); }


ul.box li:after {
left: auto;
right: 10px;
-webkit-transform: skew(15deg) rotate(6deg);
-moz-transform: skew(15deg) rotate(6deg);
-ms-transform: skew(15deg) rotate(6deg);
-o-transform: skew(15deg) rotate(6deg);
transform: skew(15deg) rotate(6deg); }