html:62.5%//10px
body:1.4rem;//14px
... <!doctype html>
<html>
<head>
<title>aaa</title>
<meta http-equiv="Cache-Control" content="no-cache, no-store, must-revalidate" />
<meta http-equiv="Pragma" content="no-cache" />
<meta http-equiv="Expires" content="0" />
<style type="text/css">
html {font-size: 62.5%;/*10 ÷ 16 × 100% = 62.5%*/}
body {font-size: 1.4rem;/*1.4 × 10px = 14px */}
p.bb {
font-size: 1.5rem;/*1.5 × 10px = 15px*/
line-height:2em;/*基于字体大小的两倍高度 2*15=30px**/
}
p.aa { font-size: 15px;/*15px*/}
</style>
</head>
<body>
你好啊
<p class="bb">你好啊nnn</p>
<p class="aa">你好啊nnn</p>
</body>
</html>
font-size rem 相比10px
line-height:2em 相比当前元素字体高度2倍