元素位置（offsetLeft[top]）

<style>
div{padding:50px;}
#box1{background: red}
#box2{background: green;position: relative}
#box3{background: pink}
/style>

<div id="box1">
<div id="box2">
<div id="box3"></div>
</div>
</div>

<script>

var box3=document.getElementById('box3');
alert(box3.offsetLeft)
// 标准下：50  ie7下：100
}
</script>