立方体没有立体效果，求解
最开始是这样：
当旋转之后就完全没有立体感了：
代码如下，一直找不到原因，哪位朋友帮忙分析一下，谢谢
<!doctype html>
<html>
<head>
<meta charset="UTF-8">
<style type="text/css">
#game {
-webkit-perspective: 800;
-webkit-perspective-origin: 50% 50%;
}
#cube {
position: relative;
width: 200px;
height: 200px;
margin: 50px auto;
-webkit-transform-style: -webkit-preserve-3d;preserve
}
.face {
position: absolute;
width: 160px;
height: 160px;
background-color: black;
color: white;
text-align: center;
font-size: 160px;
line-height: 160px;
-webkit-transition: -webkit-transform 1s linear;
}
#face2 {
-webkit-transform-origin:right;
-webkit-transform: rotateY(-90deg);
}
#face3 {
-webkit-transform-origin:left;
-webkit-transform: rotateY(90deg);
}
#face4 {
-webkit-transform-origin:top;
-webkit-transform: rotateX(-90deg);
}
#face5 {
-webkit-transform-origin:bottom;
-webkit-transform: rotateX(90deg);
}
#face6 {
-webkit-transform: translateZ(-200px);
}
#op {
width: 800px;
margin: 10px auto;
}
#op .range-control {
width:700px;
}
</style>
<script type="text/javascript">
function rotate(){
var x = document.getElementById("rotatex").value;
var y = document.getElementById("rotatey").value;
var z = document.getElementById("rotatez").value;
document.getElementById('cube').style.webkitTransform = "rotateX("+x+"deg) rotateY("+y+"deg) rotateZ("+z+"deg)";
document.getElementById('degx-span').innerText = x;
document.getElementById('degy-span').innerText = y;
document.getElementById('degz-span').innerText = z;
}
</script>
</head>
<body>
<div id="game">
<div id="cube">
<div class="face" id="face1">1</div>
<div class="face" id="face2">2</div>
<div class="face" id="face3">3</div>
<div class="face" id="face4">4</div>
<div class="face" id="face5">5</div>
<div class="face" id="face6">6</div>
</div>
</div>
<div id="op">
<p>rotate x: <span id="degx-span">0</span> deg</p>
<input type="range" min="-360" max="360" id="rotatex" value="0" class="range-control" onchange="rotate()" /><br/>
<p>rotate y: <span id="degy-span">0</span> deg</p>
<input type="range" min="-360" max="360" id="rotatey" value="0" class="range-control" onchange="rotate()" /><br/>
<p>rotate z: <span id="degz-span">0</span> deg</p>
<input type="range" min="-360" max="360" id="rotatez" value="0" class="range-control" onchange="rotate()" /><br/>
</div>
</body>
</html>
