css pseudo-class before after to achieve three-dimensional effect

div {
    width:200px;
    height:200px;
    border:1px solid #ccc;
    position: relative;
    background-color:#fff;
    float: left;
    text-align: center;
    margin: 30px;
}
.div1::after {
    z-index: -15;
    position: absolute;
    content: "";
    bottom: 14px;
    right: 7px;
    width: 36%;
    top: 59%;
    max-width: 300px;
    background: #777;
    box-shadow: 0 15px 10px #A5A5A5;
    -webkit-transform: rotate(3deg);
}
.div1::before {
    z-index: -15;
    position: absolute;
    content: "";
    bottom: 14px;
    left: 6px;
    width: 36%;
    top: 59%;
    max-width: 300px;
    background: #777;
    box-shadow: 0 15px 10px #A5A5A5;
    -webkit-transform: rotate(-3deg);
}
.div2 {
    border-bottom-right-radius: 50px;
    box-shadow: -1px 2px 2px rgba(0, 0, 0, 0.2);
}
.div2::after {
    content: '';
    width: 22px;
    height: 22px;
    position: absolute;
    bottom: 0px;
    right: 0px;
    border-radius: 0 0 16px 0;
    box-shadow: -2px -2px 5px rgba(65, 65, 65, 0.38);
    -webkit-transform: rotate(-20deg) skew(-40deg,-3deg) translate(-10px,-10px);
}
.div3 {
    border-radius: 60px / 5px;
}
.div3::after {
    z-index: -15;
    position: absolute;
    content: "";
    bottom: 2px;
    left: 4%;
    width: 91%;
    height: 10px;
    max-width: 300px;
    background: #777;
    box-shadow: 0px 4px 11px 1px #A5A5A5;
    border-radius: 50%;
}
.div3::before {
    z-index: -15;
    position: absolute;
    content: "";
    left: 4%;
    width: 91%;
    height: 10px;
    top: 4px;
    max-width: 300px;
    background: #777;
    box-shadow: 0px -4px 11px 1px #A5A5A5;
    border-radius: 50%;
}

<div class="div1">123</div>
    <div class="div2">123</div>
    <div class="div3">123</div>

http://jsfiddle.net/N93a3/

Summary:

If you use before or after, you must assign a content attribute to it and leave it empty to show the effect. Divs using pseudo-classes are generally set to position: relative; pseudo-class elements are generally set to position: absolute. To achieve the shadow effect, the box-shaw attribute of the pseudo-class element is generally used, and it is usually set behind the div and blocked by it. The border-radius of the div can be set to xxpx / xxpx to get unexpected effects.