给父元素添加border-raduis属性，并添加overflow:hidden后在ios中不显示圆角问题，给父元素添加-webkit-mask-image后解决

.banner{
  width:690rpx;
  height: 172.5rpx;
  margin: 11rpx auto 17rpx;
  overflow: hidden;
  border-radius: 15rpx;
  box-shadow: 0px 0px 10px #cecece;
 -webkit-mask-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAIAAACQd1PeAAAAGXRFWHRTb2Z0d2FyZQBBZG9iZSBJbWFnZVJlYWR5ccllPAAAAA5JREFUeNpiYGBgAAgwAAAEAAGbA+oJAAAAAElFTkSuQmCC);
 -webkit-mask-image: -webkit-radial-gradient(white, black);
}