css伪类before after 实现立体效果

p {
    width:200px;
    height:200px;
    border:1px solid #ccc;
    position: relative;
    background-color:#fff;
    float: left;
    text-align: center;
    margin: 30px;
}
.p1::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);
}
.p1::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);
}
.p2 {
    border-bottom-right-radius: 50px;
    box-shadow: -1px 2px 2px rgba(0, 0, 0, 0.2);
}
.p2::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);
}
.p3 {
    border-radius: 60px / 5px;
}
.p3::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%;
}
.p3::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%;
}

<p class="p1">123</p>
    <p class="p2">123</p>
    <p class="p3">123</p>

http://jsfiddle.net/N93a3/

总结：

如果使用before或者after必须为其赋值一个content属性，为空，才能显示出效果。使用伪类的p一般设置成position：relative；伪类元素一般设置成position：absolute。实现阴影效果一般是利用伪类元素的box-shaw属性，且一般设置在p后面，被其挡住。p的border-radius可以设置成xxpx ／ xxpx 可以得到意想不到的效果。