rem和em和px vh vw和% 移动端长度单位_html/css_WEB-ITnose
1.rem和em、px
首先来说说em和px的关系 em是指字体高度 浏览器默认1em=16px,所以0.75em=12px;我们经常会在页面上看到根元素写的font-size:65%; 这样em就成了16px*62.5=10em;这是显示在页面的字体大小是10px;
这样12px=1.2em,10px=1em,也就是说只需要将你的原来的px数值除以10，然后换上em作为单位就行了,
em的特点
em是个相对值 他会根据父级元素的大小而变化
但是如果嵌套了多个元素 要计算它的大小,是件很头疼的事情
这样的情况下,就出现了rem
rem的区别在于它是相对于根基元素的,因此不会被它的父类影响到
结论：之所以前端行业做移动端会普遍默认用rem或em,是因为可以通过js控制根元素(或者用@media)来达到适配各种分辨率的字体大小的效果
1.vh、vw和%
vh vw全称为Viewport Height和Viewport Width 意思就是视窗
很多情况下它们都是重叠的 各有优缺点 概括一下 就是
当处理宽度的时候，%单位更合适。处理高度的时候，vh单位更好。
(ps:比如你需要定位一屏内的一段文字,如果你用% 它计算的是你整个dom的高度,而vh计算的当前一屏的高度)
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