How do media queries enable responsive design?

Question

Accepted Answer

**Media queries** apply CSS conditionally based on device characteristics — most often the **viewport width** — letting one stylesheet adapt to phones, tablets, and desktops.

```css
/* base styles (mobile-first) */
.container { padding: 1rem; }

/* apply only when viewport is AT LEAST 768px wide */
@media (min-width: 768px) {
  .container { padding: 2rem; display: grid; grid-template-columns: 1fr 1fr; }
}

@media (min-width: 1024px) {
  .container { grid-template-columns: 1fr 1fr 1fr; }
}
```

## Mobile-first (min-width) vs desktop-first (max-width)

```css
/* ✅ mobile-first: base = mobile, layer on enhancements as it gets wider */
@media (min-width: 768px) { ... }

/* desktop-first: base = desktop, override down for smaller screens */
@media (max-width: 767px) { ... }
```

**Mobile-first** (`min-width`) is generally preferred: you write simple base styles for small screens, then progressively add complexity for larger ones. This tends to produce cleaner, lighter CSS and matches how content reflows.

## Other useful queries

```css
@media (max-width: 600px) { }                 /* small screens */
@media (orientation: landscape) { }            /* device orientation */
@media (prefers-color-scheme: dark) { }        /* user wants dark mode */
@media (prefers-reduced-motion: reduce) { }    /* user dislikes animation — accessibility */
@media print { }                                /* print stylesheet */
```

`prefers-reduced-motion` and `prefers-color-scheme` respond to user *preferences*, not screen size — important for accessibility and theming.

## Combining conditions

```css
@media (min-width: 768px) and (max-width: 1023px) { /* tablets only */ }
```

## A note on the future: container queries

Media queries respond to the **viewport**; the newer **container queries** (`@container`) respond to a *parent element's* size — better for truly reusable components. They complement media queries rather than replace them.

## Why it matters

Media queries are the foundation of responsive design — adapting layout, spacing, and columns to screen size.

The mobile-first `min-width` approach keeps CSS manageable, and preference queries (`prefers-reduced-motion`, `prefers-color-scheme`) extend responsiveness to accessibility and theming.