<div class="caja caja-sombra sombra1 sombra2">
       <h2>Ejemplo 5</h2>
      <p>Sombras laterales interiores</p>
    </div>

CSS

.caja{
    
    width: 200px;
    height: 150px;
    background-color: #f4f4f4;
   border-radius: 5px; 
  border: 1px dotted #9C9C9C;
}
.caja-sombra{
    position: relative;
    float: left;
    padding: 1em;
    margin: 100px 50px;
    box-shadow: 0 1px 4px rgba(0, 0, 0, 0.3), 0 0 40px rgba(0, 0, 0, 0.1) inset;
}
.caja-sombra:before, .caja-sombra:after{
    content: "";
    position: absolute;
    z-index: -2;
}
.sombra1:beforez{
    top: 10px;
    bottom: 10px;
    left: 0;
    right: 50%;
    box-shadow: 0 0 15px rgba(0,0,0,0.6);
    border-radius: 5px / 100px;
}
.sombra2:before{
    right: 0
}