<meta content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0" name="viewport"><
meta
http-equiv
=
"Content-Type"
content
=
"text/html; charset=utf-8"
/>
border-box,实际所占宽高度 = 设置的高度(height)/ 设置的宽度(width)+ 外边距(margin)
box-sizing: border-box;
display: block;去除文本对齐基线baseline还可以将父类元素font-size: 0;还可以设置vertical-align属性去掉间距