.container{display:flex;flex-wrap:wrap;width:900px;height:900px;border-left:solid 1px red;border-top:solid 1px red;background:#eee;align-items:flex-start;align-content:flex-start}.cell{width:calc(100% / 3);aspect-ratio:1 / 1;border-right:solid 1px red;border-bottom:solid 1px red}.cell:ntn-child(-n+3){border:none}