.matrix{display:inline-block;position:relative;margin:.5em}.matrix::before,.matrix::after{content:"";position:absolute;top:-4px;bottom:-4px;width:4px;border:2px solid #333}.matrix::before{left:-4px;border-right:none}.matrix::after{right:-4px;border-left:none}table{border-collapse:collapse}td input{width:50px;padding:.25em;border:1px solid #bbb;text-align:center;font-size:.9rem}