获取浏览器中的默认字体
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
<div id='foo'>
CSS default style in borwser!
</div>
<script>
var cssAll = window.getComputedStyle(document.getElementById('foo'))./*获得浏览器的全部样式*/
var css = window.getComputedStyle(document.getElementById('foo')).fontSize;
console.log(css);
</script>
</body>
</html>