CSS3的calc()用法简单介绍:
calc是calculate（计算的意思）缩写。
从calc()的外表来看，它类似于程序语言中的方法，具有计算功能。
确实如此，它可以动态的计算css中一些元素的相关属性值，能够运用简单的"+"、"-"、"*"、"/"四则运算。
基本规则如下:
（1）.可以使用百分比、px、em、rem等单位。
（2）.可以混合使用各种单位进行计算。
下面看几个代码片段:
.box{ border:1px solid #ddd; width:calc(100%-2px)} 上面的代码可以让.box元素宽度加上边框宽度正好100%，能够实现自适应效果。
.box{ width:calc(10em+20px) } 设置.box宽度为10em加20px。
下面一个完整的散列等宽全屏布局效果:
<!DOCTYPE html><html><head><meta charset=" utf-8"><meta name="author" content="http://www.softwhy.com/" /><meta name="viewport" content="width=device-width, initial-scale=1"/><title>蚂蚁部落</title><style type="text/css">*{ margin:0; padding:0;}.col-3{ width:calc(100%/3 - 5px); float:left; margin-right:calc(5px*3 /2); background:#eee; color:#333; height:100px; text-align:center; margin-bottom:calc(5px*3 /2); font-size:18px; line-height: 100px;}.col-3:nth-child(3){margin-right:0;}</style></head><body><div class="container"> <div class="col-3">1</div> <div id="antzone" class="col-3">2</div> <div class="col-3">3</div></div></body></html> 上面的代码实现了散列等宽布局效果，这里就采用calc()实现动态计算，能够实现宽度自适应。
相关阅读:
（1）.calc()可以参阅CSS3的calc()用法详解一章节。
（2）.:nth-child()可以参阅CSS的伪类选择符E:nth-child(n)一章节。
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