// 实现对角线
background: linear-gradient(to top right, transparent 0 calc(50% - 1px), #999 50%, transparent calc(50% + 1px) 100%);
// 实现对角线
background: linear-gradient(to top right, transparent 0 calc(50% - 1px), #999 50%, transparent calc(50% + 1px) 100%);