CSS div边界围绕子div

Question

1. I have one container div, which contains 3 divs inside it.
2. When i write border:1px solid red for container div, border is shown only on top of these 3 child divs, but not around them.

3. Below is css code.

    #cont { width:800px; margin-right:auto; margin-left:auto; border:1px dashed red; padding:2px; } #third, #second, #first { width:260px; float:left; margin:2px; } 

Html code:

![<div id="cont">
<div id="third"><p>A demo text </p></br>
<p>A demo text </p></br>
<p>A demo text </p></br>
<p>A demo text </p></br>
</div>

<div id="second"><p>A demo text </p></br>
<p>A demo text </p></br>
<p>A demo text </p></br>
<p>A demo text </p></br>
</div>

<div id="third"><p>A demo text </p></br>
<p>A demo text </p></br>
<p>A demo text </p></br>
<p>A demo text </p></br>
</div>
</div>][1]

Answer 1

添加溢出：隐藏;

#cont {width:800px;margin-right:auto;margin-left:auto; border:1px dashed red;padding:2px; overflow:hidden;}

Answer 2

<div style="clear:both;float:none;"></div> well solve your problem. added it under the div's

Answer 3

添加overflow：隐藏到#cont元素