CSS Container Queries have finally landed in all major browsers, revolutionizing how we think about responsive design. Instead of responding to viewport size, components can now adapt based on their container's dimensions.

Traditional responsive design relies on viewport-based media queries:

/* Traditional approach - viewport based */
@media (max-width: 768px) {
  .card {
    flex-direction: column;
  }
}

This breaks down in component-based architectures where the same component appears in different contexts - sidebar, main content, modal dialogs.