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Jun 24, 2016 am 11:33 AM

css unit

数字

　　CSS有两种数字：整数和实数(小数)

百分数

　　百分数总是相对于一个值而言

颜色

【1】关键字
　　17种合法命名颜色(标准颜色):

　　　　aqua/fuchsia/lime/olive/red/white/black/gray/maroon/orange/silver/yellow/blue/green/navy/purple/teal
　　[注意]浏览器支持140种颜色

【2】RGB模式

　　rgb(x%,y%,z%)或者rgb(a,b,c)

　　[注意1]a、b、c的范围在(0-255)

　　[注意2]若数值小于最小值0,则默认调整为0;若数值大小最大值255,则默认调整为255

【3】16进制模式

　　#abcdef

　　[注意]若16进制的3组数各自成对，则可简写为3位

　　#aabbcc <=> #abc　　//红色 red <=> rgb(255,0,0) <=> rgb(100%,0,0) <=> #ff0000 <=> #f00

【补充】

　　web安全颜色是指在256色计算机系统上总能避免抖动的颜色，表示为RGB值20%和51(相应的16进制值为33)的倍数。因此，采用16进制时，使用00\33\66\99\cc\ff认为是Web安全色。

长度

　　所有长度单位后面都有一个两字母缩写，它表示所指定的具体长度单位(长度为0时，不需要跟单位)

　　【1】绝对长度单位
　　　　英寸(in)
　　　　　　[注意]1英寸 2.54厘米 72点 6派卡
　　　　厘米(cm)
　　　　毫米(mm)
　　　　点(pt)
　　　　派卡(pc)

　　【2】相对长度单位
　　　　em -> em-height 表示一种给定字体的font-size值
　　　　ex -> x-height 表示所用字体中小写x的值，但实际中一般取em值的一半
　　　　像素(px) -> 表示计算机显示器上的一个点，点的大小取决于显示设备的分辨率

URL

　　URL分为绝对URL和相对URL，URL和开始括号之间不能有空格。如果存在空格，则整个声明都无效。

url("test.jpg")

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