SOURCE

<div id="nav">
            <ul class="nav-menu clearfix unstyled">
                <li><a href="#" class="three-d active">
                    Home
                    <span class="three-d-box"><span class="front">Home</span><span class="back">Home</span></span>
                </a></li>
                <li><a href="#" class="three-d">
                    Services
                    <span class="three-d-box"><span class="front">Services</span><span class="back">Services</span></span>
                </a></li>
                <li><a href="#" class="three-d">
                    Products
                    <span class="three-d-box"><span class="front">Products</span><span class="back">Products</span></span>
                </a></li>
                <li><a href="#" class="three-d">
                    About
                    <span class="three-d-box"><span class="front">About</span><span class="back">About</span></span>
                </a></li>
                <li><a href="#" class="three-d">
                    Contact
                    <span class="three-d-box"><span class="front">Contact</span><span class="back">Contact</span></span>
                </a></li>
                <li><a href="#" class="three-d">
                    Blog
                    <span class="three-d-box"><span class="front">Blog</span><span class="back">Blog</span></span></a>
                    <ul class="clearfix unstyled drop-menu">
                        <li><a href="#" class="three-d">
                            Html5
                            <span class="three-d-box"><span class="front">Html5</span><span class="back">Html5</span></span>
                        </a></li>
                        <li><a href="#" class="three-d">
                            Css3
                            <span class="three-d-box"><span class="front">Css3</span><span class="back">Css3</span></span>
                        </a></li>
                        <li><a href="#" class="three-d">
                            JavaScript
                            <span class="three-d-box"><span class="front">JavaScript</span><span class="back">JavaScript</span></span>
                        </a></li>
                        <li><a href="#" class="three-d">
                            Videogames
                            <span class="three-d-box"><span class="front">Videogames</span><span class="back">Videogames</span></span>
                        </a></li>
                    </ul>
                </li>
            </ul>
        </div>

 body {
            background-color: #edecec;
        }
        
        .nav-menu {
            display: block;
            background: #74adaa;
            width: 950px;
            margin: 50px auto 150px;
        }
        
        .nav-menu>li {
            display: inline;
            float: left;
            border-right: 1px solid #94c0be;
        }
        
        .nav-menu>li:last-child {
            border-right: none;
        }
        
        .nav-menu li a {
            color: #fff;
            display: block;
            text-decoration: none;
            font-smoothing: antialiased;
            text-transform: capitalize;
            overflow: visible;
            line-height: 20px;
            font-size: 20px;
            padding: 15px 30px 15px 31px;
        }
        
        .three-d {
            perspective: 200px;
            transition: all 0.7s linear;
            position: relative;
        }
        
        .three-d:not(.active):hover {
            cursor: pointer;
        }
        
        .three-d:not(.active):hover .three-d-box,
        .three-d:not(.active):focus .three-d-box {
            transform: translateZ(-25px) rotateX(90deg);
        }
        
        .three-d-box {
            transform: translateZ(-25px);
            transition: all .3s ease-out;
            transform-style: preserve-3d;
            pointer-events: none;
            position: absolute;
            top: 0;
            left: 0;
            display: block;
            width: 100%;
            height: 100%;
        }
        /*给导航设置3D前，与3D后变形效果*/
        
        .front {
            transform: rotateX(0deg) translateZ(25px);
        }
        
        .back {
            transform: rotateX(-90deg) translateZ(25px);
            color: #FFE7C4;
        }
        
        .front,
        .back {
            display: block;
            width: 100%;
            height: 100%;
            position: absolute;
            top: 0;
            left: 0;
            background: #74adaa;
            padding: 15px 30px 15px 31px;
            color: white;
            pointer-events: none;
            box-sizing: border-box;
        }
        /*设置导航当前状态与悬浮状态下的背景效果*/
        
        .nav-menu li .active .front,
        .nav-menu li .active .back,
        .nav-menu li a:hover .front,
        .nav-menu li a:hover .back {
            background-color: #51938F;
            background-size: 5px 5px;
            background-position: 0 0, 30px 30px;
            background-image: linear-gradient(45deg, #478480 25%, transparent 25%, transparent 75%, #478480 75%, #478480), linear-gradient(45deg, #478480 25%, transparent 25%, transparent 75%, #478480 75%, #478480);
        }
        
        .nav-menu ul {
            position: absolute;
            text-align: left;
            line-height: 40px;
            font-size: 14px;
            width: 200px;
            transition: all 0.3s ease-in;
            transform-origin: 0px 0px;
            transform: rotateX(-90deg);
            backface-visibility: hidden;
        }
        /*显示下拉导航菜单，并其设置一个变形效果*/
        
        .nav-menu>li:hover ul {
            display: block;
            transform: rotateX(0deg);
        }