Container queries let you style elements based on their container’s size rather than the viewport. This is huge for component-based design!

.card-container {
  container-type: inline-size;
}

@container (min-width: 400px) {
  .card {
    display: grid;
    grid-template-columns: 1fr 2fr;
  }
}

Finally, truly responsive components that don’t care where they’re placed.