SOURCE

<a class="css-3d-btn">button<a>

a.css-3d-btn{
 position: relative;
 color: rgba(255, 255, 255, 1);
 text-decoration: none;
 background-color: rgba(219, 87, 51, 1);
 font-family: "Microsoft YaHei", 微软雅黑, 宋体;
 font-weight: 700;
 font-size: 3em;
 display: block;
 padding: 4px;
 border-radius: 8px;
 /* let's use box shadows to make the button look more 3-dimensional */
 box-shadow: 0px 9px 0px rgba(219, 31, 5, 1), 0px 9px 25px rgba(0, 0, 0, .7);
 margin: 100px auto;
 width: 160px;
 text-align: center;
 -webkit-transition: all .1s ease;
 -moz-transition: all .1s ease;
 transition: all .1s ease;
}

/* now if we make the box shadows smaller when the button is clicked, it'll look like the button has been "pushed" */

a.css-3d-btn:active{
 box-shadow: 0px 3px 0px rgba(219, 31, 5, 1), 0px 3px 6px rgba(0, 0, 0, .9);
 position: relative;
 top: 6px;
}