1、简介
calc()看其外表像个函数。平时在制作页面的时候，总会碰到有的元素是100%的宽度（例如body元素）。如果元素宽度为100%时，其自身不带其他盒模型属性设置还好，要是有别的，那将导致盒子撑破。比如说，有一个边框，或者说有margin和padding，这些都会让你的盒子撑破。我们换句话来说，如果你的元素宽度是100%时，只要你在元素中添加了border,padding,margin任何一值，都将会把元素盒子撑破（标准模式下，除IE怪异模式）。平时我们碰到这样的现象时，只能通过改变结构来实现，有时甚至无法解决。就算你通过繁琐的方法实现了，但由于浏览器的兼容性而导致最终效果不一致。虽然上一篇随笔介绍的CSS3属性中的box-sizing在一定程度上解决这样的问题，但calc()函数功能实现上面的效果来得更简单。
2、语法
calc()语法非常简单，就像我们小时候学加 （+）、减（-）、乘（*）、除（/）一样，使用数学表达式来表示：
calc() = calc(四则运算)；
说明：
用于动态计算长度值。
3、浏览器兼容性
浏览器对calc()的兼容性还算不错，在IE9+、FF4.0+、Chrome19+、Safari6+都得到较好支持，同样需要在其前面加上各浏览器厂商的识别符。
（-moz-、-webkit-）
4、实例
比如要实现以下的设计图（注：图片来自百度前端技术学院2016春季班第一阶段任务三，链接：http://7xrp04.com1.z0.glb.clouddn.com/task_1_3_1.png）中的中间一栏的布局。
代码如下：
HTML：（只有中间一栏的部分布局）
<!DOCTYPE html><html lang="zh-CN"><head> <meta charset="UTF-8" /> <title>Third</title></head><body><div class="middle"> <h3 id="团队介绍">团队介绍</h3> <p><strong>黃藥師</strong>，「天下五絕」之一「東邪」。桃花島島主，黃蓉之父。黃藥師形相清癯，身材高瘦，風姿雋爽，蕭疏軒舉，湛然若神。身穿青衣直綴，頭戴同色方巾，文士模樣。個性離經叛道，狂傲不羈。性情孤僻，行動怪異，身形飄忽，有如鬼魅。「桃花影落飛神劍，碧海潮生按玉簫」是他一生武功的寫照，武功造詣非凡，已臻化境，為金庸小說中武功最絕頂的高手之一。</p> <p><strong>歐陽鋒</strong>，「天下五絕」之一「西毒」。歐陽鋒身材高大，身穿白衣，高鼻深目，臉鬚棕黃，英氣勃勃，目光如電，眼神如刀似劍，甚是鋒鋭，語聲鏗鏗似金屬之音。應為歐洲白人血統。此人兇狠毒辣，為求奪得「武功天下第一」的名號不擇手段，是金庸武俠小說中的著名反派角色和武功最絕頂的高手之一。</p> <p><strong>段智興</strong>，「天下五絕」之一「南帝」，後改稱「南僧」。法號「一燈」，一燈身穿粗布僧袍，兩道長長的白眉從眼角垂了下來，面目慈祥，眉間雖隱含愁苦，但一番雍容高華的神色。身兼「先天功」及「一陽指」兩大神功武學，功力深厚非凡。</p> <p><strong>洪七公</strong>，「天下五絕」之一「北丐」，是郭靖、黃蓉的師父，為金庸小說中武功最絕頂的高手之一。洪七公一張長方臉，頦下微須，粗手大腳，身上衣服東一塊西一塊的打滿了補釘，卻洗得乾乾淨淨，手裡拿著一根打狗棒，背上負著個朱紅漆的大葫蘆，身法迅雷不可目，「神龍見首不見尾」是他一生的寫照。</p> <p><strong>王重陽</strong>，「天下五絕」之一「中神通」。中國道教全真派創始人，被尊為全真五祖之一，原名中孚，字允卿，本金朝諸生，後為武官，改名德威，字世雄。入道後改名嚞，一名喆，字知明，道號重陽子，故稱王重陽，綽號王害瘋，京兆咸陽（今陝西省咸陽市）大魏村人。七個主要門人稱七真。</p> </div></body></html>
CSS：（只包含中间布局部分）
.middle { width: calc(100% - (80px + 120px + 200px));/*用100%的屏幕宽度减去已经知道固定的宽度，就是自适应的部分*/ overflow: auto; background-color: #FFF; border: 1px #999 solid; margin: 20px;}.middle h3,p { margin: 20px;}
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