/* Define a query container */
.card-container {
  container-type: inline-size;
  container-name: card;
}

/* Style based on container width */
@container card (min-width: 400px) {
  .card {
    display: grid;
    grid-template-columns: 200px 1fr;
  }
}

@container card (max-width: 399px) {
  .card {
    display: flex;
    flex-direction: column;
  }
}

/* Use cqi (container query inline) over cqw */
.card-title {
  /* 5% of container's inline size */
  font-size: clamp(1rem, 5cqi, 2rem);
}

.card-content {
  /* Responsive padding based on container */
  padding: 2cqi;
}

/* cqb for block dimension (height-aware containers) */
.sidebar-item {
  height: 10cqb;
}

/* Accessible fluid typography */
:root {
  /* Base font respects user preferences (rem) */
  --font-size-base: 1rem;

  /* Fluid scale with min/max bounds */
  --font-size-sm: clamp(0.875rem, 0.8rem + 0.25vw, 1rem);
  --font-size-md: clamp(1rem, 0.9rem + 0.5vw, 1.25rem);
  --font-size-lg: clamp(1.25rem, 1rem + 1vw, 2rem);
  --font-size-xl: clamp(1.5rem, 1rem + 2vw, 3rem);
  --font-size-2xl: clamp(2rem, 1rem + 3vw, 4rem);
}

h1 { font-size: var(--font-size-2xl); }
h2 { font-size: var(--font-size-xl); }
h3 { font-size: var(--font-size-lg); }
p { font-size: var(--font-size-md); }
small { font-size: var(--font-size-sm); }

/* For component-scoped fluid text */
.widget {
  container-type: inline-size;
}

.widget-title {
  /* Fluid within container, respecting user rem */
  font-size: clamp(1rem, 0.5rem + 5cqi, 2rem);
}

.widget-body {
  font-size: clamp(0.875rem, 0.5rem + 3cqi, 1.125rem);
}

/* Mobile-first: start small, add complexity */
.layout {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

/* Tablet and up */
@media (min-width: 768px) {
  .layout {
    flex-direction: row;
  }
}

/* Desktop */
@media (min-width: 1024px) {
  .layout {
    max-width: 1200px;
    margin-inline: auto;
  }
}

/* Auto-fit grid (fills available space) */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1.5rem;
}

/* Auto-fill grid (maintains minimum columns) */
.icon-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(100px, 1fr));
  gap: 1rem;
}

/* Subgrid for nested alignment */
.card {
  display: grid;
  grid-template-rows: subgrid;
  grid-row: span 3;
}

/* Query based on scroll state */
.scroll-container {
  container-type: scroll-state;
  container-name: scroller;
}

@container scroller scroll-state(scrollable: top) {
  .scroll-indicator-top {
    opacity: 0;
  }
}

@container scroller scroll-state(scrollable: bottom) {
  .scroll-indicator-bottom {
    opacity: 0;
  }
}

import { cn } from '@/lib/utils';

interface CardProps {
  title: string;
  description: string;
  image: string;
}

export function ResponsiveCard({ title, description, image }: CardProps) {
  return (
    <div className="@container">
      <article className={cn(
        "flex flex-col gap-4",
        "@md:flex-row @md:gap-6" // Container query breakpoints
      )}>
        <img
          src={image}
          alt=""
          className="w-full @md:w-48 aspect-video object-cover rounded-lg"
        />
        <div className="flex flex-col gap-2">
          <h3 className="text-[clamp(1rem,0.5rem+3cqi,1.5rem)] font-semibold">
            {title}
          </h3>
          <p className="text-[clamp(0.875rem,0.5rem+2cqi,1rem)] text-muted-foreground">
            {description}
          </p>
        </div>
      </article>
    </div>
  );
}

// @container enables container query variants (@sm, @md, @lg, etc.)
<div className="@container">
  <div className="flex flex-col @lg:flex-row @xl:gap-8">
    <div className="@sm:p-4 @md:p-6 @lg:p-8">
      Content adapts to container
    </div>
  </div>
</div>

import { useRef, useState, useEffect } from 'react';

function useContainerQuery(breakpoint: number) {
  const ref = useRef<HTMLDivElement>(null);
  const [isAbove, setIsAbove] = useState(false);

  useEffect(() => {
    const element = ref.current;
    if (!element) return;

    const observer = new ResizeObserver(([entry]) => {
      setIsAbove(entry.contentRect.width >= breakpoint);
    });

    observer.observe(element);
    return () => observer.disconnect();
  }, [breakpoint]);

  return [ref, isAbove] as const;
}

// Usage
function AdaptiveCard() {
  const [containerRef, isWide] = useContainerQuery(400);

  return (
    <div ref={containerRef}>
      {isWide ? <HorizontalLayout /> : <VerticalLayout />}
    </div>
  );
}

function ResponsiveImage({
  src,
  alt,
  sizes = "(max-width: 640px) 100vw, (max-width: 1024px) 50vw, 33vw"
}: {
  src: string;
  alt: string;
  sizes?: string;
}) {
  return (
    <picture>
      {/* Art direction with different crops */}
      <source
        media="(max-width: 640px)"
        srcSet={`${src}?w=640&aspect=1:1`}
      />
      <source
        media="(max-width: 1024px)"
        srcSet={`${src}?w=800&aspect=4:3`}
      />
      <img
        src={`${src}?w=1200`}
        alt={alt}
        sizes={sizes}
        loading="lazy"
        decoding="async"
        className="w-full h-auto object-cover"
      />
    </picture>
  );
}

/* IMPORTANT: Always include rem in fluid typography */
/* This ensures user font preferences are respected */

/* ❌ WRONG: Viewport-only ignores user preferences */
font-size: 5vw;

/* ✅ CORRECT: Include rem to respect user settings */
font-size: clamp(1rem, 0.5rem + 2vw, 2rem);

/* User zooming must still work */
@media (min-width: 768px) {
  /* Use em/rem, not px, for breakpoints in ideal world */
  /* (browsers still use px, but consider user zoom) */
}

/* ❌ NEVER: Use only viewport units for text */
.title {
  font-size: 5vw; /* Ignores user font preferences! */
}

/* ❌ NEVER: Use cqw/cqh (use cqi/cqb instead) */
.card {
  padding: 5cqw; /* cqw = container width, not logical */
}
/* ✅ CORRECT: Use logical units */
.card {
  padding: 5cqi; /* Container inline = logical direction */
}

/* ❌ NEVER: Container queries without container-type */
@container (min-width: 400px) {
  /* Won't work without container-type on parent! */
}

/* ❌ NEVER: Desktop-first media queries */
.element {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
}
@media (max-width: 768px) {
  .element {
    grid-template-columns: 1fr; /* Overriding = more CSS */
  }
}

/* ❌ NEVER: Fixed pixel breakpoints for text */
@media (min-width: 768px) {
  body { font-size: 18px; } /* Use rem! */
}

/* ❌ NEVER: Over-nesting container queries */
@container a {
  @container b {
    @container c {
      /* Too complex, reconsider architecture */
    }
  }
}