CSS3 9-10代码疑问！
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style type = "text/css">
@import url("http://www.w3cplus.com/demo/css3/base.css");
@font-face{
font-family: "myfont";
src: url("http://www.w3cplus.com/demo/css3/base.css");
}
body{
background-color: #ececec;
}
/* basic menu styles */
.nav-menu{
background: #74adaa;
width: 962px;
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;
/*调用服务器字体*/
font-family: "myfont";
-webkit-font-smoothing: antialiased;
-moz-font-smoothing: antialiased;
font-smoothing: antialiased;
text-transform: capitalize;
overflow: visible;
line-height: 20px;
font-size: 20px;
padding: 15px 30px 15px 31px;
}
.three-d{
/*设置3D舞台布景*/
position: relative;
perspective: 200px;
-webkit-perspective: 200px;
-moz-perspective: 200px;
-ms-perspective: 200px;
-o-perspective: 200px;
/*设置3D舞台布景过渡效果*/
transition: all 0.7s linear;
-webkit-transition: all 0.7s linear;
-moz-transition: all 0.7s linear;
-ms-transition: all 0.7s linear;
-o-transition: all 0.7s linear;
}
.three-d:not(.active):hover{
cursor: pointer;
}
/*给不是当前状态的3D舞台的悬浮和聚焦状态设置变形效果*/
.three-d:not(.active):hover .three-d-box,
.three-d:not(.active):focus .three-d-box{
transform: translateZ(-25px) rotateX(90deg);
-webkit-transform: translateZ(-25px) rotateX(90deg);
-moz-transform: translateZ(-25px) rotateX(90deg);
-ms-transform: translateZ(-25px) rotateX(90deg);
-o-transform: translateZ(-25px) rotateX(90deg);
}
.three-d-box{
/*给3D舞台中的“three-d-box”设置变形和过渡效果*/
position: absolute;
top: 0;
left: 0;
display: block;
width: 100%;
height: 100%;
transform: translateZ(-25px);
-webkit-transform: translateZ(-25px);
-moz-transform: translateZ(-25px);
-ms-transform: translateZ(-25px);
-o-transform: translateZ(-25px);
transition: all 0.3s ease-out;
-webkit-transition: all 0.3s ease-out;
-moz-transition: all 0.3s ease-out;
-ms-transition: all 0.3s ease-out;
-o-transition: all 0.3s ease-out;
transform-style: preserve-3d;
-webkit-transform-style: preserve-3d;
-moz-transform-style: preserve-3d;
-ms-transform-style: preserve-3d;
-o-transform-style: preserve-3d;
pointer-events: none;
-webkit-pointer-events: none;
-moz-pointer-events: none;
-ms-pointer-events: none;
-o-pointer-events: none;
}
/*给导航设置3D前、3D后的变形效果*/
.front{
transform: rotateX(0deg) translateZ(25px);
-webkit-transform: rotateX(0deg) translateZ(25px);
-moz-transform: rotateX(0deg) translateZ(25px);
-ms-transform: rotateX(0deg) translateZ(25px);
-o-transform: rotateX(0deg) translateZ(25px);
}
.back{
transform: rotateX(-90deg) translateZ(25px);
-webkit-transform: rotateX(-90deg) translateZ(25px);
-moz-transform: rotateX(-90deg) translateZ(25px);
-ms-transform: rotateX(-90deg) translateZ(25px);
-o-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;
-webkit-pointer-events: none;
-moz-pointer-events: none;
-ms-pointer-events: none;
-o-pointer-events: none;
pointer-events: none;
-webkit-box-sizing: border-box;
box-sizing: border-box;
}
/*设置导航当前状态和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: #51938F;
background-size: 5px 5px;/*如果值设置一个值，这个值是宽度，高度自适应*/
background-image: -webkit-linear-gradient(45deg, #478480 25%, transparent 25%, transparent 75%, #478480 75%, #478480),
linear-gradient(45deg, #478480 25%, transparent 25%, transparent 75%, #478480 75%, #478480);
background-image: -moz-linear-gradient(45deg, #478480 25%, transparent 25%, transparent 75%, #478480 75%, #478480),
linear-gradient(45deg, #478480 25%, transparent 25%, transparent 75%, #478480 75%, #478480);
background-image: -ms-linear-gradient(45deg, #478480 25%, transparent 25%, transparent 75%, #478480 75%, #478480),
linear-gradient(45deg, #478480 25%, transparent 25%, transparent 75%, #478480 75%, #478480);
background-image: -o-linear-gradient(45deg, #478480 25%, transparent 25%, transparent 75%, #478480 75%, #478480),
linear-gradient(45deg, #478480 25%, transparent 25%, transparent 75%, #478480 75%, #478480);
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;
-webkit-transition: all 0.3s ease-in;
-moz-transition: all 0.3s ease-in;
-ms-transition: all 0.3s ease-in;
-o-transition: all 0.3s ease-in;
transform-origin: 0px 0px;
-webkit-transform-origin: 0px 0px;
-moz-transform-origin: 0px 0px;
-ms-transform-origin: 0px 0px;
-o-transform-origin: 0px 0px;
transform: rotateX(-90deg);
-webkit-transform: rotateX(-90deg);
-moz-transform: rotateX(-90deg);
-ms-transform: rotateX(-90deg);
-o-transform: rotateX(-90deg);
backface-visibility: hidden;
-webkit-backface-visibility: hidden;
-moz-backface-visibility: hidden;
-ms-backface-visibility: hidden;
-o-backface-visibility: hidden;
}
.nav-menu li:hover ul{
transform: rotateX(0deg);
-webkit-transform: rotateX(0deg);
-moz-transform: rotateX(0deg);
-ms-transform: rotateX(0deg);
-o-transform: rotateX(0deg);
}
</style>
</head>
<body>
<div id="nav">
<ul class="nav-menu clearfix unstyled">
<li><a href="#" class="three-d active">
Home
<span><span>Home</span><span>Home</span></span>
</a></li>
<li><a href="#">
Services
<span><span>Services</span><span>Services</span></span>
</a></li>
<li><a href="#">
Products
<span><span>Products</span><span>Products</span></span>
</a></li>
<li><a href="#">
About
<span><span>About</span><span>About</span></span>
</a></li>
<li><a href="#">
Contact
<span><span>Contact</span><span>Contact</span></span>
</a></li>
<li><a href="#">
Blog
<span><span>Blog</span><span>Blog</span></span></a>
<ul class="clearfix unstyled drop-menu">
<li><a href="#">
Html5
<span><span>Html5</span><span>Html5</span></span>
</a></li>
<li><a href="#">
Css3
<span><span>Css3</span><span>Css3</span></span>
</a></li>
<li><a href="#">
JavaScript
<span><span>JavaScript</span><span>JavaScript</span></span>
</a></li>
<li><a href="#">
Videogames
<span><span>Videogames</span><span>Videogames</span></span>
</a></li>
</ul>
</li>
<li><a href="#">
Shop On-line
<span><span>Shop On-line</span><span>Shop On-line</span></span>
</a></li>
</ul>
</div>
</body>
</html>
提问： three-d-box 沿着Z轴向里移动25px, front,back沿着Z轴向外移动25px, “25px”的这个值是怎么计算出来的！
