02Box model comparison — a card that shows whether border and padding count toward its size

<main class="stage">
<div class="wrap is-demo" id="wrap">
  <div class="track" id="track">
    <div class="guide" id="guide"></div>
    <div class="row">
      <span class="rowLabel">border-box</span>
      <div class="box borderBox" id="borderBox"></div>
    </div>
    <div class="row">
      <span class="rowLabel">content-box</span>
      <div class="box contentBox" id="contentBox"></div>
    </div>
  </div>
  <input class="widthRange" id="widthRange" type="range" min="120" max="200" value="140" aria-label="Declared width">
  <div class="readout" id="readout">Declared width —px</div>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;

// 계산 겹은 index.html 의 apply() 에 있다 — 선언 너비를 실제 style.width 로 넣고
// getBoundingClientRect 로 다시 잰 실제 렌더 너비를 이론값(선언+테두리·패딩)과 나란히 보여준다.
// 여기는 두 박스의 테두리·패딩 값과 안내선 모양만 맡는다.
@include stage($stage-yellow);

$border-w: 8px;
$pad-w: 12px;

.wrap {
  width: 280px;
  display: flex;
  flex-direction: column;
  gap: $sp-3;
  align-items: center;
}

.track {
  position: relative;
  width: 260px;
  display: flex;
  flex-direction: column;
  gap: $sp-3;
  padding-top: $sp-2;
}

.guide {
  position: absolute;
  top: 0;
  left: 0;
  width: 2px;
  height: 100%;
  background: repeating-linear-gradient($subject-ink, $subject-ink 4px, transparent 4px, transparent 8px);
  transform: translateX(140px);
}

.row {
  display: flex;
  align-items: center;
  gap: $sp-2;
}

.rowLabel {
  width: 76px;
  flex: 0 0 auto;
  color: $subject-ink;
  font-size: 11px;
  font-weight: 700;
}

.box {
  height: 34px;
  border: $border-w solid $subject-ink;
  padding: 0 $pad-w;
  background: rgba($subject-blue, .38);
  transition: width $dur-base $ease-out;
  box-sizing: content-box;
}

.contentBox {
  box-sizing: content-box;
  background: rgba($subject-orange-deep, .28);
}

.borderBox {
  box-sizing: border-box;
}

.widthRange {
  width: 260px;
  accent-color: $subject-blue-deep;
}

.readout {
  color: $subject-ink;
  font-size: 11px;
  text-align: center;
}

@media (max-width: 340px) {
  .wrap { width: 230px; gap: $sp-2; }
  .track, .widthRange { width: 210px; gap: $sp-2; }
  .rowLabel { width: 64px; font-size: 10px; }
  .box { height: 28px; }
}

@media (prefers-reduced-motion: reduce) {
  // reduce: 자동 루프의 사인 진동만 멈춘다(슬라이더로 하는 실사용 조작은 그대로 즉시 반영)
  .box { transition: none; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.wrap {
  width: 280px;
  display: flex;
  flex-direction: column;
  gap: 12px;
  align-items: center;
}

.track {
  position: relative;
  width: 260px;
  display: flex;
  flex-direction: column;
  gap: 12px;
  padding-top: 8px;
}

.guide {
  position: absolute;
  top: 0;
  left: 0;
  width: 2px;
  height: 100%;
  background: repeating-linear-gradient(#17141a, #17141a 4px, transparent 4px, transparent 8px);
  transform: translateX(140px);
}

.row {
  display: flex;
  align-items: center;
  gap: 8px;
}

.rowLabel {
  width: 76px;
  flex: 0 0 auto;
  color: #17141a;
  font-size: 11px;
  font-weight: 700;
}

.box {
  height: 34px;
  border: 8px solid #17141a;
  padding: 0 12px;
  background: rgba(47, 109, 246, 0.38);
  transition: width 300ms ease-out;
  box-sizing: content-box;
}

.contentBox {
  box-sizing: content-box;
  background: rgba(201, 48, 0, 0.28);
}

.borderBox {
  box-sizing: border-box;
}

.widthRange {
  width: 260px;
  accent-color: #0a4fe8;
}

.readout {
  color: #17141a;
  font-size: 11px;
  text-align: center;
}

@media (max-width: 340px) {
  .wrap {
    width: 230px;
    gap: 8px;
  }
  .track, .widthRange {
    width: 210px;
    gap: 8px;
  }
  .rowLabel {
    width: 64px;
    font-size: 10px;
  }
  .box {
    height: 28px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .box {
    transition: none;
  }
}

(function () {
  var BORDER_PX = 8;
  var PADDING_PX = 12;
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var wrap = document.getElementById('wrap');
  var track = document.getElementById('track');
  var guide = document.getElementById('guide');
  var borderBox = document.getElementById('borderBox');
  var contentBox = document.getElementById('contentBox');
  var widthRange = document.getElementById('widthRange');
  var readout = document.getElementById('readout');
  var isDemo = true;
  var declared = 140;

  function human() { if (isDemo) { wrap.classList.remove('is-demo'); isDemo = false; } }
  widthRange.addEventListener('input', function () {
    human();
    declared = Number(widthRange.value);
  });
  widthRange.addEventListener('pointerdown', human);

  function apply() {
    borderBox.style.width = declared + 'px';
    contentBox.style.width = declared + 'px';
    // 실측 — 계산값을 가정하지 않고 실제 렌더 결과를 다시 잰다
    var bRect = borderBox.getBoundingClientRect();
    var cRect = contentBox.getBoundingClientRect();
    guide.style.transform = 'translateX(' + declared + 'px)';
    widthRange.value = String(Math.round(declared));
    // 이론값 = Declared width + 테두리·패딩 두 변 — 실측(getBoundingClientRect)과 맞는지 함께 보여준다
    var theory = declared + 2 * (BORDER_PX + PADDING_PX);
    readout.textContent = 'Declared ' + Math.round(declared) + 'px · border-box actual ' +
      Math.round(bRect.width) + 'px · content-box actual ' + Math.round(cRect.width) +
      'px (theoretical ' + Math.round(theory) + 'px)';
  }

  var start = 0;
  function loop(ts) {
    if (!start) start = ts;
    if (isDemo && !reduce) {
      declared = 160 + 38 * Math.sin((ts - start) / 900);
    }
    apply();
    requestAnimationFrame(loop);
  }
  requestAnimationFrame(loop);
})();

// BoxModel — vanilla 판(run/376/demo/02-box-model/index.html) 의 React 포트.
// 슬라이더로 선언 너비를 바꾸면 border-box·content-box 두 박스에 같은 width 를 넣고,
// 실제 렌더 결과(getBoundingClientRect)를 이론값(선언+테두리·패딩)과 나란히 보여준다.
import { useEffect, useRef } from "react";
import styles from "./BoxModel.module.scss";

type Box<T> = { current: T };

const BORDER_PX = 8;
const PADDING_PX = 12;

export default function BoxModel() {
  const wrapRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const guideRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const borderBoxRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const contentBoxRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const widthRangeRef = useRef(null) as unknown as Box<HTMLInputElement>;
  const readoutRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const rafRef = useRef(0) as unknown as Box<number>;

  useEffect(() => {
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const wrap = wrapRef.current;
    const guide = guideRef.current;
    const borderBox = borderBoxRef.current;
    const contentBox = contentBoxRef.current;
    const widthRange = widthRangeRef.current;
    const readout = readoutRef.current;
    if (!wrap || !guide || !borderBox || !contentBox || !widthRange || !readout) return;

    let isDemo = true;
    let declared = 140;

    function human() { if (isDemo) { wrap!.classList.remove(styles.isDemo); isDemo = false; } }
    function onInput() { human(); declared = Number(widthRange!.value); }
    function onPointerDown() { human(); }
    widthRange.addEventListener("input", onInput);
    widthRange.addEventListener("pointerdown", onPointerDown);

    function apply() {
      borderBox!.style.width = declared + "px";
      contentBox!.style.width = declared + "px";
      const bRect = borderBox!.getBoundingClientRect();
      const cRect = contentBox!.getBoundingClientRect();
      guide!.style.transform = "translateX(" + declared + "px)";
      widthRange!.value = String(Math.round(declared));
      const theory = declared + 2 * (BORDER_PX + PADDING_PX);
      readout!.textContent = "선언 " + Math.round(declared) + "px · border-box 실제 " +
        Math.round(bRect.width) + "px · content-box 실제 " + Math.round(cRect.width) +
        "px (이론값 " + Math.round(theory) + "px)";
    }

    let start = 0;
    function loop(ts: number) {
      if (!start) start = ts;
      if (isDemo && !reduce) { declared = 160 + 38 * Math.sin((ts - start) / 900); }
      apply();
      rafRef.current = requestAnimationFrame(loop);
    }
    rafRef.current = requestAnimationFrame(loop);

    return () => {
      widthRange!.removeEventListener("input", onInput);
      widthRange!.removeEventListener("pointerdown", onPointerDown);
      cancelAnimationFrame(rafRef.current);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.wrap + " " + styles.isDemo} ref={wrapRef}>
        <div className={styles.track}>
          <div className={styles.guide} ref={guideRef}></div>
          <div className={styles.row}>
            <span className={styles.rowLabel}>border-box</span>
            <div className={styles.box + " " + styles.borderBox} ref={borderBoxRef}></div>
          </div>
          <div className={styles.row}>
            <span className={styles.rowLabel}>content-box</span>
            <div className={styles.box + " " + styles.contentBox} ref={contentBoxRef}></div>
          </div>
        </div>
        <input className={styles.widthRange} ref={widthRangeRef} type="range" min="120" max="200" defaultValue="140" aria-label="선언 너비" />
        <div className={styles.readout} ref={readoutRef}>선언 너비 —px</div>
      </div>
    </main>
  );
}