尝试使用flexbox模型。写起来既简单又简短。

现场杰斯菲德尔

CSS:

#wrapper {
  display: flex;
  border: 1px solid black;
}
#first {
    border: 1px solid red;
}
#second {
    border: 1px solid green;
}

默认方向为行。因此，它们在#包装器中彼此对齐。 但它不支持IE9或更低版本

你可以使用CSS float属性将元素放在一起:

#first {
float: left;
}
#second {
float: left;
}

你需要确保包装div允许浮动的宽度，和空白等设置正确。

下面是解决方案:

#wrapper {
    width: 500px;
    border: 1px solid black;
    overflow: auto; /* so the size of the wrapper is alway the size of the longest content */
}
#first {
    float: left;
    width: 300px;
    border: 1px solid red;
}
#second {
    border: 1px solid green;
    margin: 0 0 0 302px; /* considering the border you need to use a margin so the content does not float under the first div*/
}

你的演示版本更新了;

http://jsfiddle.net/dqC8t/1/

我的方法:

<div class="left">Left</div>
<div class="right">Right</div>

CSS:

.left {
    float: left;
    width: calc(100% - 200px);
    background: green;
}

.right {
    float: right;
    width: 200px;
    background: yellow;
}

#wrapper { width: 1200; border: 1px solid black; position: relative; float: left; } #first { width: 300px; border: 1px solid red; position: relative; float: left; } #second { border: 1px solid green; position: relative; float: left; width: 500px; } <div id="wrapper"> <div id="first">Stack Overflow is for professional and enthusiast programmers, people who write code because they love it.</div> <div id="second">When you post a new question, other users will almost immediately see it and try to provide good answers. This often happens in a matter of minutes, so be sure to check back frequently when your question is still new for the best response.</div> </div>

尝试使用下面的代码更改来将两个div放在彼此前面

#wrapper {
  width: 500px;
  border: 1px solid black;
  display:flex;
}

JSFiddle link