@media (max-width: 720px) {
  .nav {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    width: 100%;
    box-sizing: border-box;
  }

  .nav button {
    min-width: 0;
    padding: 0.8rem 0.2rem;
    text-align: center;
  }
}