单位

1rem = 1*根元素font-size px rem与px 场景：图片占位符

1em = 1*相对父类font-size px em与px

1vw = 可视窗口的宽度的1% vw与% 场景：图片占位符 100% 100%/3.5 = 28.57% 1vw = 1% 28.57% = 28.57vw

1vw = 可视窗口的宽度的1% vw与px 场景：图片占位符 1400px 1400px*1% = 14px

1rpx = 0.5px rpx与px 场景：小程序