#matrix { display: flex; flex-direction: column; gap: 2px; } .row { display: flex; width: 254px; gap: 2px; } .led { width: 30px; height: 30px; border: 1px solid gray; background-color: whitesmoke; cursor: pointer; border-radius: 2px; } .led.on { background-color: blue; } button { width: 100px; margin-top: 1rem; /* flex: 1 1 auto; */ }