Hand-built websites that load fast.

<div class="faq">
  <!-- Sharing a name makes these an exclusive accordion -->
  <details name="faq" open>
    <summary>What's on this page that needs no JavaScript?</summary>
    <p>This accordion, the popover below and the form's validation.
      All of it is plain HTML that the browser already knows how to run.</p>
  </details>
  <details name="faq">
    <summary>Why lean on the platform?</summary>
    <p>Native elements arrive accessible, keyboard-ready and fast.
      Every line of script you don't write is a bug you don't ship.</p>
  </details>
  <details name="faq">
    <summary>Does it work with a screen reader?</summary>
    <p>Yes. Semantics come built in, so assistive tech gets the
      right roles and states for free.</p>
  </details>
</div>

<button type="button" popovertarget="hello" class="button ghost">
  Open a popover
</button>
<div id="hello" popover>
  <p><strong>Hello from the top layer.</strong> Light dismiss, focus
    handling and Esc to close all come free with <code>popover</code>.</p>
  <button type="button" popovertarget="hello" popovertargetaction="hide"
    class="button primary">Got it</button>
</div>

<div class="signup">
  <label for="demo-email">Email</label>
  <input id="demo-email" type="email" required
    placeholder="you@example.com" autocomplete="off">
  <p class="hint">Type something that isn't an email, then click away.</p>
</div>

/* The stage is resizable; the card inside only knows its container. */
.cq-stage {
  container: profile / inline-size;
  resize: horizontal;
  overflow: hidden;
  inline-size: 100%;
  min-inline-size: 13rem;
  max-inline-size: 100%;
  padding: 1.25rem;
  border: 1px dashed var(--color-border-strong);
  border-radius: var(--radius-lg);
}

/* Registering the property lets the browser animate an angle. */
@property --angle {
  syntax: "<angle>";
  inherits: false;
  initial-value: 0deg;
}

.profile {
  --ring: var(--color-border);
  display: grid;
  gap: 1rem;
  justify-items: center;
  padding: 1.5rem;
  text-align: center;
  border: 2px solid transparent;
  border-radius: var(--radius-lg);
  background:
    linear-gradient(var(--color-surface), var(--color-surface)) padding-box,
    conic-gradient(from var(--angle), var(--ring), var(--ring)) border-box;
  transition: box-shadow 0.4s;

  & .avatar {
    display: grid;
    place-items: center;
    inline-size: clamp(3.5rem, 18cqi, 5.5rem);
    aspect-ratio: 1;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--color-brand), var(--color-accent));
    color: var(--color-on-brand);
    font: 400 clamp(1.1rem, 6cqi, 1.75rem) / 1 var(--font-display);
  }

  & h4 { font-size: clamp(1.1rem, 5cqi, 1.5rem); }
  & p { color: var(--color-muted); font-size: 0.875rem; }

  & .stats {
    display: none;
    gap: 1.5rem;
    padding: 0;
    list-style: none;
    font-size: 0.8rem;
    color: var(--color-muted);

    & b {
      display: block;
      font: 400 1.4rem / 1.2 var(--font-display);
      color: var(--color-text);
    }
  }

  /* :has() lets a child's state style its parent, no script needed */
  &:has(.pin input:checked) {
    --ring: var(--color-brand), var(--color-accent), var(--color-brand);
    animation: spin 3s linear infinite;
    box-shadow: 0 0 2.5rem -0.5rem var(--color-glow);
  }
}

@keyframes spin {
  to { --angle: 360deg; }
}

/* Medium container: avatar beside the name */
@container profile (inline-size > 24rem) {
  .profile {
    grid-template-columns: auto 1fr;
    justify-items: start;
    text-align: start;

    & .pin { grid-column: 1 / -1; }
  }
}

/* Wide container: the stats appear */
@container profile (inline-size > 36rem) {
  .profile {
    grid-template-columns: auto 1fr auto;
    align-items: center;

    & .stats { display: flex; }
  }
}

/**
 * Conway's Game of Life on a <canvas>.
 *
 * The grid is two flat Uint8Arrays swapped every generation, so a step
 * allocates nothing. The canvas tracks its container with a
 * ResizeObserver, renders at device-pixel resolution, and pauses itself
 * when scrolled out of view.
 */
export function initLife(root: HTMLElement) {
	const canvas = root.querySelector<HTMLCanvasElement>("canvas")!;
	const ctx = canvas.getContext("2d")!;
	const playBtn = root.querySelector<HTMLButtonElement>("[data-life=play]")!;
	const genOut = root.querySelector<HTMLOutputElement>("[data-life=gen]")!;
	const popOut = root.querySelector<HTMLOutputElement>("[data-life=pop]")!;
	const speed = root.querySelector<HTMLInputElement>("[data-life=speed]")!;

	const CELL = 12;
	let cols = 0;
	let rows = 0;
	let cells = new Uint8Array(0);
	let next = new Uint8Array(0);
	let generation = 0;
	let running = false;
	let visible = true;
	let last = 0;

	const reduceMotion = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
	let colors = readColors();

	// Theme colours are light-dark() pairs, which canvas can't parse. Reading
	// them back through a real property resolves them to plain colours.
	function readColors() {
		const probe = document.createElement("span");
		root.appendChild(probe);
		const resolve = (name: string) => {
			probe.style.color = `var(${name})`;
			return getComputedStyle(probe).color;
		};
		const result = { live: resolve("--life-live"), grid: resolve("--life-grid") };
		probe.remove();
		return result;
	}

	function resize() {
		const dpr = window.devicePixelRatio || 1;
		const { width, height } = canvas.getBoundingClientRect();
		canvas.width = Math.round(width * dpr);
		canvas.height = Math.round(height * dpr);
		ctx.setTransform(dpr, 0, 0, dpr, 0, 0);

		const newCols = Math.max(1, Math.floor(width / CELL));
		const newRows = Math.max(1, Math.floor(height / CELL));
		if (newCols === cols && newRows === rows) return draw();

		// Keep whatever overlaps the old grid, so resizing never wipes the board
		const resized = new Uint8Array(newCols * newRows);
		for (let y = 0; y < Math.min(rows, newRows); y++) {
			for (let x = 0; x < Math.min(cols, newCols); x++) {
				resized[y * newCols + x] = cells[y * cols + x];
			}
		}
		cols = newCols;
		rows = newRows;
		cells = resized;
		next = new Uint8Array(cols * rows);
		draw();
	}

	function randomize(density = 0.28) {
		for (let i = 0; i < cells.length; i++) cells[i] = Math.random() < density ? 1 : 0;
		generation = 0;
		draw();
	}

	function step() {
		for (let y = 0; y < rows; y++) {
			for (let x = 0; x < cols; x++) {
				let n = 0;
				// Wrap around the edges: the board is a torus
				for (let dy = -1; dy <= 1; dy++) {
					const row = ((y + dy + rows) % rows) * cols;
					for (let dx = -1; dx <= 1; dx++) {
						if (dx || dy) n += cells[row + ((x + dx + cols) % cols)];
					}
				}
				const i = y * cols + x;
				next[i] = n === 3 || (n === 2 && cells[i]) ? 1 : 0;
			}
		}
		[cells, next] = [next, cells];
		generation++;
		draw();
	}

	function draw() {
		const w = cols * CELL;
		const h = rows * CELL;
		ctx.clearRect(0, 0, canvas.width, canvas.height);

		ctx.fillStyle = colors.grid;
		for (let x = 0; x <= cols; x++) ctx.fillRect(x * CELL, 0, 1, h);
		for (let y = 0; y <= rows; y++) ctx.fillRect(0, y * CELL, w, 1);

		let population = 0;
		ctx.fillStyle = colors.live;
		for (let i = 0; i < cells.length; i++) {
			if (!cells[i]) continue;
			population++;
			const x = (i % cols) * CELL;
			const y = Math.floor(i / cols) * CELL;
			ctx.beginPath();
			ctx.roundRect(x + 2, y + 2, CELL - 3, CELL - 3, 3);
			ctx.fill();
		}
		genOut.value = generation.toLocaleString();
		popOut.value = population.toLocaleString();
	}

	function loop(time: number) {
		if (!running) return;
		const interval = 1000 / Number(speed.value);
		if (visible && time - last >= interval) {
			last = time;
			step();
		}
		requestAnimationFrame(loop);
	}

	function setRunning(on: boolean) {
		running = on;
		playBtn.textContent = on ? "Pause" : "Play";
		playBtn.setAttribute("aria-pressed", String(on));
		if (on) requestAnimationFrame(loop);
	}

	// Paint cells by dragging; the first cell touched decides paint or erase
	let paintValue: number | null = null;
	function cellAt(e: PointerEvent) {
		const rect = canvas.getBoundingClientRect();
		const x = Math.floor((e.clientX - rect.left) / CELL);
		const y = Math.floor((e.clientY - rect.top) / CELL);
		return x >= 0 && y >= 0 && x < cols && y < rows ? y * cols + x : -1;
	}
	canvas.addEventListener("pointerdown", (e) => {
		const i = cellAt(e);
		if (i < 0) return;
		canvas.setPointerCapture(e.pointerId);
		paintValue = cells[i] ? 0 : 1;
		cells[i] = paintValue;
		draw();
	});
	canvas.addEventListener("pointermove", (e) => {
		if (paintValue === null) return;
		const i = cellAt(e);
		if (i >= 0 && cells[i] !== paintValue) {
			cells[i] = paintValue;
			draw();
		}
	});
	const stopPaint = () => (paintValue = null);
	canvas.addEventListener("pointerup", stopPaint);
	canvas.addEventListener("pointercancel", stopPaint);

	playBtn.addEventListener("click", () => setRunning(!running));
	root.querySelector("[data-life=step]")!.addEventListener("click", () => {
		setRunning(false);
		step();
	});
	root.querySelector("[data-life=random]")!.addEventListener("click", () => randomize());
	root.querySelector("[data-life=clear]")!.addEventListener("click", () => {
		setRunning(false);
		cells.fill(0);
		generation = 0;
		draw();
	});

	new ResizeObserver(resize).observe(canvas);
	new IntersectionObserver(([entry]) => (visible = entry.isIntersecting)).observe(canvas);

	// Re-read the palette when the theme flips
	new MutationObserver(() => {
		colors = readColors();
		draw();
	}).observe(document.documentElement, { attributes: true, attributeFilter: ["class"] });
	window
		.matchMedia("(prefers-color-scheme: dark)")
		.addEventListener("change", () => ((colors = readColors()), draw()));

	resize();
	randomize();
	if (!reduceMotion) setRunning(true);
}