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HTML/CSSIntermediate#css#responsive
Media queries apply CSS conditionally based on viewport size, orientation, or device features. Mobile-first means writing base styles for small screens first, then progressively enhancing with min-width breakpoints for larger screens.
.card { width: 100%; }
@media (min-width: 768px) {
.card { width: 50%; }
}
@media (min-width: 1024px) {
.card { width: 33.33%; }
}