css单位总结: body的font-size:14px body第二代子元素的font-size:em: 1.2em=1.2*1.2*14pxrem:1.2rem=1.2*14px 视口高度:1000px 视口宽度:500px vh:1vh=1000px/100vw:1vw=500px/100vmin:vmin=500px/100vmax:vmax=100