07行が変わっても先頭に残らない縦の区切り線

<main class="stage">
<div class="dv is-demo" id="dvRoot">
  <div class="dv__card" id="dvCard">
    <ul class="dv__list" id="dvList">
      <li class="dv__item">ホーム</li>
      <li class="dv__item">デザイン</li>
      <li class="dv__item">コード</li>
      <li class="dv__item">サンプル</li>
      <li class="dv__item">レビュー</li>
      <li class="dv__item">お問い合わせ</li>
      <li class="dv__item">もっと見る</li>
    </ul>
  </div>
  <label class="dv__ctrl">
    <span>幅</span>
    <input type="range" id="dvRange" min="150" max="336" value="336">
    <span class="dv__meta"><span class="dv__tag">ROWS</span> <b id="dvRows">1</b></span>
  </label>
</div>
</main>

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

// 핵심: 항목 앞 세로 선은 줄 맨 앞 항목(is-first)에서만 JS 판정으로 숨긴다.

$sep-gap: 12px;
$sep-h: 20px;

@include stage($stage-ink);

.dv {
  width: min(100%, 360px);
  display: grid;
  gap: $sp-2;
  justify-items: center;
}

.dv__card {
  box-sizing: border-box;
  width: 336px;
  max-width: 100%;
  min-height: 96px;
  padding: $sp-4;
  display: grid;
  align-content: center;
  border-radius: $r-card;
  background: $tick-panel;
}

.dv__list {
  margin: 0;
  padding: 0;
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: $sp-3 0;
}

.dv__item {
  position: relative;
  padding: 0 var(--sep-gap, #{$sep-gap});
  color: $stage-paper;
  font-size: 14px;
  font-weight: 700;
  line-height: 24px;
}
.dv__item::before {
  content: "";
  position: absolute;
  left: 0;
  top: 50%;
  width: 2px;
  height: var(--sep-h, #{$sep-h});
  border-radius: $r-pill;
  background: $subject-sky;
  transform: translateY(-50%);
}
.dv__item.is-first { padding-left: 0; }
.dv__item.is-first::before { opacity: 0; }

.dv__ctrl {
  box-sizing: border-box;
  width: 100%;
  display: flex;
  align-items: center;
  gap: $sp-3;
  font-size: 12px;
  line-height: 16px;
  color: rgba($stage-paper, .78);
}
.dv__ctrl input { flex: 1; min-width: 0; accent-color: $subject-sky; }

.dv__meta { display: flex; align-items: baseline; gap: $sp-2; }
.dv__tag { font-weight: 700; letter-spacing: .08em; }
.dv__meta b { min-width: 2ch; text-align: right; font-variant-numeric: tabular-nums; color: $stage-paper; }

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

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.dv {
  width: min(100%, 360px);
  display: grid;
  gap: 8px;
  justify-items: center;
}

.dv__card {
  box-sizing: border-box;
  width: 336px;
  max-width: 100%;
  min-height: 96px;
  padding: 16px;
  display: grid;
  align-content: center;
  border-radius: 16px;
  background: #231f28;
}

.dv__list {
  margin: 0;
  padding: 0;
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: 12px 0;
}

.dv__item {
  position: relative;
  padding: 0 var(--sep-gap, 12px);
  color: #ffffff;
  font-size: 14px;
  font-weight: 700;
  line-height: 24px;
}

.dv__item::before {
  content: "";
  position: absolute;
  left: 0;
  top: 50%;
  width: 2px;
  height: var(--sep-h, 20px);
  border-radius: 999px;
  background: #6ec8ff;
  transform: translateY(-50%);
}

.dv__item.is-first {
  padding-left: 0;
}

.dv__item.is-first::before {
  opacity: 0;
}

.dv__ctrl {
  box-sizing: border-box;
  width: 100%;
  display: flex;
  align-items: center;
  gap: 12px;
  font-size: 12px;
  line-height: 16px;
  color: rgba(255, 255, 255, 0.78);
}

.dv__ctrl input {
  flex: 1;
  min-width: 0;
  accent-color: #6ec8ff;
}

.dv__meta {
  display: flex;
  align-items: baseline;
  gap: 8px;
}

.dv__tag {
  font-weight: 700;
  letter-spacing: 0.08em;
}

.dv__meta b {
  min-width: 2ch;
  text-align: right;
  font-variant-numeric: tabular-nums;
  color: #ffffff;
}

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

(function () {
  // 기법: 항목마다 앞에 세로 선(::before)을 두고, 줄이 바뀐 항목은 JS 가 offsetTop 을 앞 항목과 비교해 is-first 를 붙여 선을 숨긴다.
  // 폭이 바뀔 때마다 다시 판정하므로 어느 폭에서도 줄 맨 앞에 선이 남지 않는다. (CSS 만으로는 줄 시작을 알 수 없다.)
  var SEP_GAP = 12;
  var SEP_H_PX = 20;
  var CYCLE_MS = 2000;
  var NARROW_PX = 150;
  var WIDE_PX = 336;

  var root = document.getElementById('dvRoot');
  var card = document.getElementById('dvCard');
  var list = document.getElementById('dvList');
  var range = document.getElementById('dvRange');
  var rowsEl = document.getElementById('dvRows');
  var items = Array.prototype.slice.call(list.children);
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  function mark() {
    var rows = 0;
    var lastTop = null;
    items.forEach(function (li) {
      var top = li.offsetTop;
      var first = lastTop === null || top !== lastTop;
      if (first) rows += 1;
      li.classList.toggle('is-first', first);
      lastTop = top;
    });
    rowsEl.textContent = String(rows);
  }
  function setWidth(px) {
    card.style.width = px.toFixed(1) + 'px';
    range.value = String(Math.round(px));
    mark();
  }
  function stopDemo() { root.classList.remove('is-demo'); }

  range.addEventListener('input', function () {
    stopDemo();
    setWidth(Number(range.value));
  });

  var t0 = null;
  function tick(ts) {
    if (t0 === null) t0 = ts;
    if (root.classList.contains('is-demo')) {
      var phase = ((ts - t0) % CYCLE_MS) / CYCLE_MS;
      var wave = 0.5 + 0.5 * Math.cos(phase * Math.PI * 2);
      setWidth(NARROW_PX + (WIDE_PX - NARROW_PX) * wave);
    }
    requestAnimationFrame(tick);
  }

  card.style.setProperty('--sep-gap', SEP_GAP + 'px');
  card.style.setProperty('--sep-h', SEP_H_PX + 'px');
  setWidth(WIDE_PX);
  if (reduce) {
    stopDemo();
  } else {
    requestAnimationFrame(tick);
  }
})();

// WrapSeparator — vanilla 판(07-divl-vertical-wrap-aware-separator) 의 React 포트.
// 항목 앞 세로 선은 줄 맨 앞 항목(is-first)에서만 JS 가 offsetTop 비교로 숨긴다.
import { useEffect, useRef } from "react";
import styles from "./WrapSeparator.module.scss";

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

const SEP_GAP = 12;
const SEP_H_PX = 20;
const CYCLE_MS = 2000;
const NARROW_PX = 150;
const WIDE_PX = 336;
const LABELS: string[] = ["홈", "디자인", "코드", "예제", "후기", "문의", "더보기"];

export default function WrapSeparator() {
  const cardRef = useRef<HTMLDivElement | null>(null) as Box<HTMLDivElement | null>;
  const listRef = useRef<HTMLUListElement | null>(null) as Box<HTMLUListElement | null>;
  const rangeRef = useRef<HTMLInputElement | null>(null) as Box<HTMLInputElement | null>;
  const rowsRef = useRef<HTMLElement | null>(null) as Box<HTMLElement | null>;

  useEffect(() => {
    const card = cardRef.current;
    const list = listRef.current;
    const range = rangeRef.current;
    const rowsEl = rowsRef.current;
    if (!card || !list || !range || !rowsEl) return;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const items = Array.from(list.children) as HTMLElement[];
    const firstClass = styles.first;
    let demo = !reduce;
    let t0: number | null = null;
    let raf = 0;

    const mark = (): void => {
      let rows = 0;
      let lastTop: number | null = null;
      items.forEach((li) => {
        const top = li.offsetTop;
        const first = lastTop === null || top !== lastTop;
        if (first) rows += 1;
        li.classList.toggle(firstClass, first);
        lastTop = top;
      });
      rowsEl.textContent = String(rows);
    };
    const setWidth = (px: number): void => {
      card.style.width = px.toFixed(1) + "px";
      range.value = String(Math.round(px));
      mark();
    };
    const onInput = (): void => {
      demo = false;
      setWidth(Number(range.value));
    };
    range.addEventListener("input", onInput);

    function tick(ts: number): void {
      if (t0 === null) t0 = ts;
      if (demo) {
        const phase = ((ts - t0) % CYCLE_MS) / CYCLE_MS;
        const wave = 0.5 + 0.5 * Math.cos(phase * Math.PI * 2);
        setWidth(NARROW_PX + (WIDE_PX - NARROW_PX) * wave);
      }
      raf = requestAnimationFrame(tick);
    }

    card.style.setProperty("--sep-gap", SEP_GAP + "px");
    card.style.setProperty("--sep-h", SEP_H_PX + "px");
    setWidth(WIDE_PX);
    if (!reduce) raf = requestAnimationFrame(tick);
    return () => {
      cancelAnimationFrame(raf);
      range.removeEventListener("input", onInput);
    };
  }, []);

  return (
    <div className={styles.dv}>
      <div className={styles.card} ref={cardRef}>
        <ul className={styles.list} ref={listRef}>
          {LABELS.map((label) => (
            <li key={label} className={styles.item}>{label}</li>
          ))}
        </ul>
      </div>
      <label className={styles.ctrl}>
        <span>폭</span>
        <input type="range" min={150} max={336} defaultValue={336} ref={rangeRef} />
        <span className={styles.meta}>
          <span className={styles.tag}>ROWS</span> <b ref={rowsRef}>1</b>
        </span>
      </label>
    </div>
  );
}