“的margin-top：汽车” 不工作

Question

<div id="home"> 
    <div id="fix">aaa<br />fff</div> 
    <div id="text">bvvvbbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb bbb </div> 
</div> 

#fix { 
    width: 500px; 
    position: fixed; 
    background-color: blue; 
    top:0; 
    left:0; 
} 
#text { 
    background-color: green; 
    margin-top:auto; 
    width: 500px; 
    height: 700px; 
} 

为什么在这个例子中不margin-top工作？

（在div#fix，用PHP自动生成的数据。）

演示：http://jsfiddle.net/uK2RK/9/

编辑：现在DIV＃修复盖div的＃文本。我可以设置margin-top，但我不知道它有多少行，但是这是使用PHP自动生成的。

Answer 1

它的工作原理应该是这样的（你没有说你认为认为它应该工作）。

作为每一个的auto块级非替换元件在正常流动与overflow: visible（默认）值（如一个div）（它是#text）的CSS 2.1 specification一个margin-top的部分10.6.3被视为margin-top: 0。

因此，该元素在正常流程中位于0像素（除非有其他边距/填充正在播放，其中没有）离开前一个元素的底部。由于前一个元素（#fix）为position: fixed，因此不在正常流程中，因此不存在这样的元素，因此#text将从其容器顶部（#home）放置0像素。这个位置正好在#fix下面。