如下圖，一點都不圓，大家?guī)臀铱纯次业拇a是否有問題html <div class="box"></div>css.box{    position: relative;    width: 300px;    height: 140px;    background: red;}.box:before{    content: '';    position: absolute;    left: 0;    top: 0;    bottom: 0;    width: 20px;    background: radial-gradient(farthest-corner, #fff 50%, transparent 0%);    background-size: 20px 20px;    background-repeat: repeat-y;}.box:after{    content: '';    position: absolute;    right: 0;    top: 0;    bottom: 0;    width: 20px;    background: radial-gradient(farthest-corner, #fff 50%, transparent 0%);    background-size: 20px 20px;    background-repeat: repeat-y;}