05Flex gap fallback — spacing that falls back to margins when the gap property isn't applied

<main class="stage">
<div class="wrap is-demo" id="wrap">
  <div class="head">
    <input class="addInput" id="addInput" type="text" placeholder="Type a tag, press Enter" maxlength="8">
    <button class="simToggle" id="simToggle" type="button" aria-pressed="false">Simulate fallback</button>
  </div>
  <ul class="chipRow" id="chipRow">
    <li class="chip">margin</li>
    <li class="chip">token</li>
    <li class="chip">align</li>
  </ul>
  <span class="modeLabel" id="modeLabel">gap mode</span>
</div>
</main>

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

// 계산 겹은 칩 등장 애니메이션의 --i 기반 시차(stagger)에 있다 — index.html 이 칩마다 순서를
// CSS 변수로 넘긴다. 여기는 두 간격 표기법(margin 폴백 · gap 지원)과 등장 곡선만 맡는다.
@include stage($stage-paper);

.wrap {
  width: 260px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-3;
}

.head {
  display: flex;
  align-items: center;
  gap: $sp-2;
  width: 100%;
}

.addInput {
  flex: 1 1 auto;
  min-width: 0;
  border: none;
  border-radius: $r-control;
  background: $subject-cream;
  color: $subject-ink;
  padding: $sp-1 $sp-2;
  font-size: 11px;

  &::placeholder { color: rgba($subject-ink, .45); }
  &:focus-visible { outline: 2px solid $subject-blue-light; outline-offset: 2px; }
}

.simToggle {
  flex: 0 0 auto;
  appearance: none;
  border: none;
  border-radius: $r-pill;
  background: $subject-ink;
  color: $subject-cream;
  padding: $sp-1 $sp-2;
  font-size: 10px;
  font-weight: 600;
  cursor: pointer;
  transition: transform $dur-instant $ease-out;

  &:active { transform: scale(.96); }
  &[aria-pressed="true"] { background: $subject-orange-deep; }
  &:focus-visible { outline: 2px solid $subject-blue-light; outline-offset: 2px; }
}

.chipRow {
  display: flex;
  flex-wrap: wrap;
  width: 100%;
  min-height: 34px;
  margin: 0;
  padding: 0;
  list-style: none;

  // 폴백: gap 을 모르는 환경 — 마지막 칩만 빼고 오른쪽 여백을 준다. 항상 선언, 아래 @supports 가 지원판에서 덮는다
  > .chip:not(:last-child) { margin-right: $sp-2; }
}

@supports (gap: 1rem) {
  .wrap:not(.force-fallback) .chipRow {
    gap: $sp-2;

    > .chip:not(:last-child) { margin-right: 0; }
  }
}

.chip {
  appearance: none;
  border: none;
  border-radius: $r-pill;
  background: $subject-blue;
  color: $subject-cream;
  padding: $sp-2 $sp-4;
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  transform: scale(1);
  transition: transform $dur-enter $ease-elastic;
  transition-delay: calc(var(--i, 0) * 40ms);

  &:hover { transform: scale(1.08); }
}

.chip.is-entering { transform: scale(0); transition-duration: $dur-base; }
.chip.is-leaving { transform: scale(0); transition-delay: 0ms; }

.modeLabel {
  color: $subject-ink;
  font-size: 10px;
  font-weight: 700;
}

@media (max-width: 340px) {
  .wrap { width: 220px; }
  .chipRow { min-height: 30px; }
}

@media (prefers-reduced-motion: reduce) {
  .chip { transition: none; }
  .simToggle { transition: none; }
}

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

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

.wrap {
  width: 260px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
}

.head {
  display: flex;
  align-items: center;
  gap: 8px;
  width: 100%;
}

.addInput {
  flex: 1 1 auto;
  min-width: 0;
  border: none;
  border-radius: 12px;
  background: #fff7e6;
  color: #17141a;
  padding: 4px 8px;
  font-size: 11px;
}
.addInput::placeholder {
  color: rgba(23, 20, 26, 0.45);
}
.addInput:focus-visible {
  outline: 2px solid #5b8cf8;
  outline-offset: 2px;
}

.simToggle {
  flex: 0 0 auto;
  appearance: none;
  border: none;
  border-radius: 999px;
  background: #17141a;
  color: #fff7e6;
  padding: 4px 8px;
  font-size: 10px;
  font-weight: 600;
  cursor: pointer;
  transition: transform 140ms ease-out;
}
.simToggle:active {
  transform: scale(0.96);
}
.simToggle[aria-pressed=true] {
  background: #c93000;
}
.simToggle:focus-visible {
  outline: 2px solid #5b8cf8;
  outline-offset: 2px;
}

.chipRow {
  display: flex;
  flex-wrap: wrap;
  width: 100%;
  min-height: 34px;
  margin: 0;
  padding: 0;
  list-style: none;
}
.chipRow > .chip:not(:last-child) {
  margin-right: 8px;
}

@supports (gap: 1rem) {
  .wrap:not(.force-fallback) .chipRow {
    gap: 8px;
  }
  .wrap:not(.force-fallback) .chipRow > .chip:not(:last-child) {
    margin-right: 0;
  }
}
.chip {
  appearance: none;
  border: none;
  border-radius: 999px;
  background: #2f6df6;
  color: #fff7e6;
  padding: 8px 16px;
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  transform: scale(1);
  transition: transform 600ms cubic-bezier(0.34, 1.56, 0.64, 1);
  transition-delay: calc(var(--i, 0) * 40ms);
}
.chip:hover {
  transform: scale(1.08);
}

.chip.is-entering {
  transform: scale(0);
  transition-duration: 300ms;
}

.chip.is-leaving {
  transform: scale(0);
  transition-delay: 0ms;
}

.modeLabel {
  color: #17141a;
  font-size: 10px;
  font-weight: 700;
}

@media (max-width: 340px) {
  .wrap {
    width: 220px;
  }
  .chipRow {
    min-height: 30px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .chip {
    transition: none;
  }
  .simToggle {
    transition: none;
  }
}

(function () {
  var STEP_MS = 380; // 자동 추가/삭제 gap
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var wrap = document.getElementById('wrap');
  var chipRow = document.getElementById('chipRow');
  var addInput = document.getElementById('addInput');
  var simToggle = document.getElementById('simToggle');
  var modeLabel = document.getElementById('modeLabel');
  var isDemo = true;

  function human() { if (isDemo) { wrap.classList.remove('is-demo'); isDemo = false; } }

  var seq = 0;
  function addChip(text) {
    var li = document.createElement('li');
    li.className = 'chip is-entering';
    li.textContent = text;
    li.style.setProperty('--i', String(seq % 6));
    seq += 1;
    li.addEventListener('click', function () { human(); removeChip(li); });
    chipRow.appendChild(li);
    requestAnimationFrame(function () {
      requestAnimationFrame(function () { li.classList.remove('is-entering'); });
    });
  }

  function removeChip(li) {
    if (!li || li.classList.contains('is-leaving')) return;
    li.classList.add('is-leaving');
    li.addEventListener('transitionend', function () { li.remove(); }, { once: true });
  }

  addInput.addEventListener('keydown', function (e) {
    if (e.key !== 'Enter') return;
    human();
    var value = addInput.value.trim();
    if (value) { addChip(value); addInput.value = ''; }
  });

  var simOn = false;
  function setSim(on) {
    simOn = on;
    wrap.classList.toggle('force-fallback', on);
    simToggle.setAttribute('aria-pressed', String(on));
    modeLabel.textContent = on ? 'margin fallback' : 'gap mode';
  }
  simToggle.addEventListener('click', function () { human(); setSim(!simOn); });

  var WORDS = ['align', 'gap', 'rule', 'token', 'flow'];
  var wi = 0;
  var last = 0;
  var phase = 0;
  function loop(ts) {
    if (!last) last = ts;
    if (isDemo && !reduce && ts - last >= STEP_MS) {
      last = ts;
      phase = (phase + 1) % 3;
      if (phase === 0) {
        addChip(WORDS[wi % WORDS.length]);
        wi += 1;
      } else if (phase === 1 && chipRow.children.length > 2) {
        removeChip(chipRow.lastElementChild);
      } else {
        setSim(!simOn);
      }
    }
    requestAnimationFrame(loop);
  }
  requestAnimationFrame(loop);
})();

// GapFlexOld — vanilla 판(run/375/demo/05-compat-gap-flex-old/index.html) 의 React 포트.
// 폴백은 항상 margin-right 로 간격을 주고, @supports(gap) 지원판에서 gap 이 그 역할을 넘겨받는다.
import { useEffect, useRef } from "react";
import styles from "./GapFlexOld.module.scss";

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

const STEP_MS = 380; // 자동 추가/삭제 간격

export default function GapFlexOld() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const chipRowRef = useRef(null) as unknown as Box<HTMLUListElement>;
  const addInputRef = useRef(null) as unknown as Box<HTMLInputElement>;
  const simToggleRef = useRef(null) as unknown as Box<HTMLButtonElement>;
  const modeLabelRef = useRef(null) as unknown as Box<HTMLSpanElement>;
  const rafRef = useRef(0) as unknown as Box<number>;

  useEffect(() => {
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const wrap = rootRef.current;
    const chipRow = chipRowRef.current;
    const addInput = addInputRef.current;
    const simToggle = simToggleRef.current;
    const modeLabel = modeLabelRef.current;
    if (!wrap || !chipRow || !addInput || !simToggle || !modeLabel) return;

    let isDemo = true;

    function human() { if (isDemo) { wrap!.classList.remove(styles.isDemo); isDemo = false; } }

    let seq = 0;
    function addChip(text: string) {
      const li = document.createElement("li");
      li.className = styles.chip + " " + styles.isEntering;
      li.textContent = text;
      li.style.setProperty("--i", String(seq % 6));
      seq += 1;
      li.addEventListener("click", function () { human(); removeChip(li); });
      chipRow!.appendChild(li);
      requestAnimationFrame(function () {
        requestAnimationFrame(function () { li.classList.remove(styles.isEntering); });
      });
    }

    function removeChip(li: Element | null) {
      if (!li || li.classList.contains(styles.isLeaving)) return;
      li.classList.add(styles.isLeaving);
      li.addEventListener("transitionend", function () { (li as HTMLElement).remove(); }, { once: true });
    }

    function onKeydown(e: KeyboardEvent) {
      if (e.key !== "Enter") return;
      human();
      const value = addInput!.value.trim();
      if (value) { addChip(value); addInput!.value = ""; }
    }
    addInput.addEventListener("keydown", onKeydown);

    let simOn = false;
    function setSim(on: boolean) {
      simOn = on;
      wrap!.classList.toggle(styles.forceFallback, on);
      simToggle!.setAttribute("aria-pressed", String(on));
      modeLabel!.textContent = on ? "margin 폴백판" : "gap 지원판";
    }
    function onSimClick() { human(); setSim(!simOn); }
    simToggle.addEventListener("click", onSimClick);

    const WORDS = ["정렬", "간격", "규칙", "토큰", "흐름"];
    let wi = 0;
    let last = 0;
    let phase = 0;
    function loop(ts: number) {
      if (!last) last = ts;
      if (isDemo && !reduce && ts - last >= STEP_MS) {
        last = ts;
        phase = (phase + 1) % 3;
        if (phase === 0) {
          addChip(WORDS[wi % WORDS.length]);
          wi += 1;
        } else if (phase === 1 && chipRow!.children.length > 2) {
          removeChip(chipRow!.lastElementChild);
        } else {
          setSim(!simOn);
        }
      }
      rafRef.current = requestAnimationFrame(loop);
    }
    rafRef.current = requestAnimationFrame(loop);

    return () => {
      addInput!.removeEventListener("keydown", onKeydown);
      simToggle!.removeEventListener("click", onSimClick);
      cancelAnimationFrame(rafRef.current);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.wrap + " " + styles.isDemo} ref={rootRef}>
        <div className={styles.head}>
          <input className={styles.addInput} ref={addInputRef} type="text" placeholder="태그 입력 후 Enter" maxLength={8} />
          <button className={styles.simToggle} ref={simToggleRef} type="button" aria-pressed="false">폴백 흉내내기</button>
        </div>
        <ul className={styles.chipRow} ref={chipRowRef}>
          <li className={styles.chip}>여백</li>
          <li className={styles.chip}>토큰</li>
          <li className={styles.chip}>정렬</li>
        </ul>
        <span className={styles.modeLabel} ref={modeLabelRef}>gap 지원판</span>
      </div>
    </main>
  );
}