為什么after不設(shè)置position就無(wú)法設(shè)置box-shadow？請(qǐng)問(wèn)是什么原理啊。*{padding: 0;margin: 0}.wrap{width: 200px;height: 200px;position: relative;background: blue}.wrap::after{position: absolute;content: '';width: 100px;box-shadow: 0 10px 0 2px #f33433,0 20px 0 2px #f33433,0 30px 0 2px #f33433}這段css代碼如果after不設(shè)置position就會(huì)變得無(wú)效