3 CSS с отзывчивой столбцей CSS

.container {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr; /*fraction*/
}

.section {
  border: 1px solid;
}

@media (max-width: 768px) { /*breakpoint*/
  .container {
    grid-template-columns: none;
  }
}
Dangerous Dragonfly