:root {
  --cell-border-color: #7f8c8d;
}

* {
  padding: 0;
  margin: 0;
  box-sizing: border-box;
}

body {
  /* https://uigradients.com/#Zinc */
  background: linear-gradient(to right, #ada996, #f2f2f2, #dbdbdb, #eaeaea);
}

.container {
  max-width: 720px;
  margin: 0 auto;
}

.change-grid-size-btn {
  font-size: 20px;
  color: #333;
  padding: 8px 16px;
  background-color: #fff;
  display: block;
  border: 1px solid var(--cell-border-color);
  margin: 30px auto 30px;
  cursor: pointer;
}

.change-grid-size-btn:hover {
  background-color: #ebebeb;
}

.grid {
  border: 1px solid var(--cell-border-color);
  background-color: #fff;
}

.row {
  display: flex;
}

.cell {
  flex: 1;
  aspect-ratio: 1 / 1;
  border: 1px solid var(--cell-border-color);
}