01Dropzone highlight that never flickers over child elements

<main class="stage">
<div class="dz is-demo" id="dzRoot">
  <div class="dz__zone" id="dzZone" role="button" tabindex="0" aria-label="Drop the file here">
    <span class="dz__ring" aria-hidden="true"></span>
    <span class="dz__icon" aria-hidden="true">
      <svg viewBox="0 0 256 256" width="26" height="26"><g fill="currentColor"><path d="M240 128a80 80 0 0 1-80 80H72A56 56 0 1 1 85.92 97.74v.1A80 80 0 0 1 240 128" opacity=".2"/><path d="M178.34 165.66L160 147.31V208a8 8 0 0 1-16 0v-60.69l-18.34 18.35a8 8 0 0 1-11.32-11.32l32-32a8 8 0 0 1 11.32 0l32 32a8 8 0 0 1-11.32 11.32M160 40a88.08 88.08 0 0 0-78.71 48.68A64 64 0 1 0 72 216h40a8 8 0 0 0 0-16H72a48 48 0 0 1 0-96c1.1 0 2.2 0 3.29.12A88 88 0 0 0 72 128a8 8 0 0 0 16 0a72 72 0 1 1 100.8 66a8 8 0 0 0 3.2 15.34a7.9 7.9 0 0 0 3.2-.68A88 88 0 0 0 160 40"/></g></svg>
    </span>
    <span class="dz__label">Drop the file here</span>
    <span class="dz__badge" id="dzBadge" aria-hidden="true">Overlap <b class="dz__n"></b></span>
  </div>
  <div class="dz__bar">
    <span class="dz__meta">dragenter · dragleave · dataTransfer</span>
  </div>
</div>
</main>

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

// 드롭존 하이라이트(01) — 움직임은 CSS keyframes 두 개뿐이다(링 opacity·scale / 카운터 정수).
// 실사용 경로는 JS 가 depth 카운터로 --n 을 직접 setProperty 한다 — 데모 루프와 같은 변수를 공유한다.

@property --n {
  syntax: "<integer>";
  inherits: false;
  initial-value: 0;
}

@include stage($stage-ink);

$dz-panel:  #211d26;
$dz-text:   $subject-cream;
$dz-ring:   $subject-sky;
$dz-badge:  #2a2432;

$duration: $dur-loop;
$easing: $ease-out;
$color: $dz-ring;

.dz {
  --dz-ring: #{$dz-ring};
  position: relative;
  display: flex; flex-direction: column;
  width: 100%; height: 100%; min-height: 164px;
  overflow: hidden;
}

.dz__zone {
  position: relative;
  margin: $sp-3 $sp-3 0;
  flex: 1;
  display: flex; flex-direction: column; align-items: center; justify-content: center;
  gap: $sp-2;
  border-radius: $r-card;
  border: 2px dashed rgba($dz-text, .28);
  background: rgba($dz-panel, .6);
  cursor: pointer;
}
.dz__zone:focus-visible { outline: 2px solid $dz-ring; outline-offset: 2px; }

.dz__ring {
  position: absolute; inset: 0;
  border-radius: $r-card;
  border: 2px solid $dz-ring;
  opacity: 0;
  transform: scale(.94);
  pointer-events: none;
}
.dz__zone.is-over .dz__ring {
  opacity: 1;
  transform: scale(1);
  transition: opacity $dur-quick $easing, transform $dur-quick $ease-elastic;
}
.dz__zone.is-dropped .dz__ring {
  opacity: 1;
  transform: scale(1.08);
  transition: opacity $dur-quick $easing, transform $dur-instant $ease-elastic;
}

.dz__icon {
  position: relative; z-index: 1;
  display: flex;
  color: rgba($dz-text, .82);
}

.dz__label {
  position: relative; z-index: 1;
  font-weight: 600; font-size: clamp(10px, 2.6vw, 12px); line-height: 1.3;
  color: $dz-text;
  text-align: center;
  padding: 0 $sp-3;
}

.dz__badge {
  position: relative; z-index: 1;
  display: inline-flex; align-items: center; gap: 4px;
  padding: $sp-1 $sp-2;
  border-radius: $r-pill;
  background: rgba($dz-badge, .92);
  font-weight: 600; font-size: 10px; line-height: 1.2;
  color: rgba($dz-text, .82);
  opacity: 0;
  --n: 0;
}
.dz__zone.is-over .dz__badge { opacity: 1; transition: opacity $dur-quick $easing; }

.dz__n { counter-reset: dzn var(--n); }
.dz__n::before { content: counter(dzn); }

.dz__bar {
  display: flex; justify-content: flex-end;
  padding: $sp-2 $sp-3 $sp-3;
}
.dz__meta {
  font-size: 10px; font-weight: 500; color: rgba($dz-text, .72);
}

// ── 데모 루프 — 진입 깊이(depth)가 0→3 을 오르내리는 동안 테두리는 한 번만 켜지고 한 번만 꺼진다 ──
@keyframes dzRing {
  0%   { opacity: 0; transform: scale(.94); }
  8%   { opacity: 1; transform: scale(1.06); animation-timing-function: $ease-elastic; }
  18%  { transform: scale(1); animation-timing-function: $easing; }
  54%  { opacity: 1; transform: scale(1); }
  60%  { opacity: 1; transform: scale(1.08); }
  70%  { opacity: 0; transform: scale(.96); }
  100% { opacity: 0; transform: scale(.94); }
}
@keyframes dzCount {
  0%, 6%   { --n: 0; opacity: 0; }
  10%      { --n: 1; opacity: 1; }
  22%      { --n: 2; }
  34%      { --n: 3; }
  44%      { --n: 2; }
  52%      { --n: 1; }
  58%, 100% { --n: 0; opacity: 0; }
}

.is-demo .dz__ring {
  animation-name: dzRing;
  animation-duration: $duration;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}
.is-demo .dz__badge {
  animation-name: dzCount;
  animation-duration: $duration;
  animation-timing-function: linear;
  animation-iteration-count: infinite;
}

@media (max-width: 340px) {
  .dz__label { font-size: 10px; }
}

@media (prefers-reduced-motion: reduce) {
  .is-demo .dz__ring, .is-demo .dz__badge { animation: none !important; opacity: 0 !important; }
}

@property --n {
  syntax: "<integer>";
  inherits: false;
  initial-value: 0;
}
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);
}

.dz {
  --dz-ring: #6ec8ff;
  position: relative;
  display: flex;
  flex-direction: column;
  width: 100%;
  height: 100%;
  min-height: 164px;
  overflow: hidden;
}

.dz__zone {
  position: relative;
  margin: 12px 12px 0;
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 8px;
  border-radius: 16px;
  border: 2px dashed rgba(255, 247, 230, 0.28);
  background: rgba(33, 29, 38, 0.6);
  cursor: pointer;
}

.dz__zone:focus-visible {
  outline: 2px solid #6ec8ff;
  outline-offset: 2px;
}

.dz__ring {
  position: absolute;
  inset: 0;
  border-radius: 16px;
  border: 2px solid #6ec8ff;
  opacity: 0;
  transform: scale(0.94);
  pointer-events: none;
}

.dz__zone.is-over .dz__ring {
  opacity: 1;
  transform: scale(1);
  transition: opacity 220ms ease-out, transform 220ms cubic-bezier(0.34, 1.56, 0.64, 1);
}

.dz__zone.is-dropped .dz__ring {
  opacity: 1;
  transform: scale(1.08);
  transition: opacity 220ms ease-out, transform 140ms cubic-bezier(0.34, 1.56, 0.64, 1);
}

.dz__icon {
  position: relative;
  z-index: 1;
  display: flex;
  color: rgba(255, 247, 230, 0.82);
}

.dz__label {
  position: relative;
  z-index: 1;
  font-weight: 600;
  font-size: clamp(10px, 2.6vw, 12px);
  line-height: 1.3;
  color: #fff7e6;
  text-align: center;
  padding: 0 12px;
}

.dz__badge {
  position: relative;
  z-index: 1;
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 4px 8px;
  border-radius: 999px;
  background: rgba(42, 36, 50, 0.92);
  font-weight: 600;
  font-size: 10px;
  line-height: 1.2;
  color: rgba(255, 247, 230, 0.82);
  opacity: 0;
  --n: 0;
}

.dz__zone.is-over .dz__badge {
  opacity: 1;
  transition: opacity 220ms ease-out;
}

.dz__n {
  counter-reset: dzn var(--n);
}

.dz__n::before {
  content: counter(dzn);
}

.dz__bar {
  display: flex;
  justify-content: flex-end;
  padding: 8px 12px 12px;
}

.dz__meta {
  font-size: 10px;
  font-weight: 500;
  color: rgba(255, 247, 230, 0.72);
}

@keyframes dzRing {
  0% {
    opacity: 0;
    transform: scale(0.94);
  }
  8% {
    opacity: 1;
    transform: scale(1.06);
    animation-timing-function: cubic-bezier(0.34, 1.56, 0.64, 1);
  }
  18% {
    transform: scale(1);
    animation-timing-function: ease-out;
  }
  54% {
    opacity: 1;
    transform: scale(1);
  }
  60% {
    opacity: 1;
    transform: scale(1.08);
  }
  70% {
    opacity: 0;
    transform: scale(0.96);
  }
  100% {
    opacity: 0;
    transform: scale(0.94);
  }
}
@keyframes dzCount {
  0%, 6% {
    --n: 0;
    opacity: 0;
  }
  10% {
    --n: 1;
    opacity: 1;
  }
  22% {
    --n: 2;
  }
  34% {
    --n: 3;
  }
  44% {
    --n: 2;
  }
  52% {
    --n: 1;
  }
  58%, 100% {
    --n: 0;
    opacity: 0;
  }
}
.is-demo .dz__ring {
  animation-name: dzRing;
  animation-duration: 2s;
  animation-timing-function: ease-out;
  animation-iteration-count: infinite;
}

.is-demo .dz__badge {
  animation-name: dzCount;
  animation-duration: 2s;
  animation-timing-function: linear;
  animation-iteration-count: infinite;
}

@media (max-width: 340px) {
  .dz__label {
    font-size: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .is-demo .dz__ring, .is-demo .dz__badge {
    animation: none !important;
    opacity: 0 !important;
  }
}

// 드롭존 하이라이트 — 자식 요소를 넘나드는 dragenter·dragleave 쌍은 한 번의 진입에 여러 번 발생한다.
// 카운터 depth 를 두어 depth 가 0보다 클 때만 하이라이트하면 자식 경계를 넘어도 테두리가 깜빡이지 않는다.
(function () {
  var root = document.getElementById('dzRoot');
  var zone = document.getElementById('dzZone');
  var badge = document.getElementById('dzBadge');
  if (!root || !zone || !badge) return;
  var depth = 0;

  function paint() {
    zone.classList.toggle('is-over', depth > 0);
    badge.style.setProperty('--n', depth);
  }
  function enter(e) { e.preventDefault(); depth += 1; paint(); }
  function leave(e) { e.preventDefault(); depth = Math.max(0, depth - 1); paint(); }
  function over(e) { e.preventDefault(); }
  function drop(e) {
    e.preventDefault();
    var fileCount = (e.dataTransfer && e.dataTransfer.files) ? e.dataTransfer.files.length : 0;
    depth = 0; paint();
    zone.setAttribute('data-drop-count', String(fileCount));
    zone.classList.add('is-dropped');
    setTimeout(function () { zone.classList.remove('is-dropped'); }, 640);
  }
  function live() { root.classList.remove('is-demo'); }
  zone.addEventListener('dragenter', enter);
  zone.addEventListener('dragleave', leave);
  zone.addEventListener('dragover', over);
  zone.addEventListener('drop', drop);
  ['pointerdown', 'focusin'].forEach(function (ev) { zone.addEventListener(ev, live); });
})();

// UploadProgressDropzoneHighlight — vanilla 판(run/329/demo/01-upload-progress-dropzone-highlight/index.html) 의 React 포트.
// 자식 요소를 넘나드는 dragenter·dragleave 쌍은 한 번의 진입에 여러 번 발생한다. 카운터 depth 를 두어
// depth 가 0보다 클 때만 하이라이트하면 자식 경계를 넘어도 테두리가 깜빡이지 않는다.
import { useRef, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./UploadProgressDropzoneHighlight.module.scss";

export type UploadProgressDropzoneHighlightProps = {
  duration?: string;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
type NVars = CSSProperties & { "--n"?: number };
type Box<T> = { current: T };
type DragEvt = { preventDefault: () => void; dataTransfer?: { files?: { length: number } } | null };

const LABEL = "파일을 여기로 끌어와 놓으세요";
const BADGE_PREFIX = "겹침";
const META = "dragenter · dragleave · dataTransfer";

export default function UploadProgressDropzoneHighlight({
  duration = "2s",
  easing = "ease-out",
  color = "#6ec8ff"
}: UploadProgressDropzoneHighlightProps) {
  const [demo, setDemo] = useState(true);
  const [depth, setDepth] = useState(0);
  const [dropped, setDropped] = useState(false);
  const dropTimer = useRef(0) as Box<number>;
  const vars: Vars = { "--duration": duration, "--easing": easing, "--color": color };
  const badgeVars: NVars = { "--n": depth };

  function live(): void {
    setDemo(false);
  }
  function enter(e: DragEvt): void {
    e.preventDefault();
    setDepth((d) => d + 1);
  }
  function leave(e: DragEvt): void {
    e.preventDefault();
    setDepth((d) => Math.max(0, d - 1));
  }
  function over(e: DragEvt): void {
    e.preventDefault();
  }
  function drop(e: DragEvt): void {
    e.preventDefault();
    setDepth(0);
    setDropped(true);
    window.clearTimeout(dropTimer.current);
    dropTimer.current = window.setTimeout(() => setDropped(false), 640);
  }

  const rootCls = demo ? `${styles.dz} ${styles.isDemo}` : styles.dz;
  const zoneCls = [styles.zone, depth > 0 ? styles.isOver : "", dropped ? styles.isDropped : ""].filter(Boolean).join(" ");

  return (
    <main className={styles.stage}>
      <div className={rootCls} style={vars}>
        <div
          className={zoneCls}
          role="button"
          tabIndex={0}
          aria-label={LABEL}
          onDragEnter={enter}
          onDragLeave={leave}
          onDragOver={over}
          onDrop={drop}
          onPointerDown={live}
          onFocus={live}
        >
          <span className={styles.ring} aria-hidden="true"></span>
          <span className={styles.icon} aria-hidden="true">
            <svg viewBox="0 0 256 256" width="26" height="26"><g fill="currentColor"><path d="M240 128a80 80 0 0 1-80 80H72A56 56 0 1 1 85.92 97.74v.1A80 80 0 0 1 240 128" opacity=".2"/><path d="M178.34 165.66L160 147.31V208a8 8 0 0 1-16 0v-60.69l-18.34 18.35a8 8 0 0 1-11.32-11.32l32-32a8 8 0 0 1 11.32 0l32 32a8 8 0 0 1-11.32 11.32M160 40a88.08 88.08 0 0 0-78.71 48.68A64 64 0 1 0 72 216h40a8 8 0 0 0 0-16H72a48 48 0 0 1 0-96c1.1 0 2.2 0 3.29.12A88 88 0 0 0 72 128a8 8 0 0 0 16 0a72 72 0 1 1 100.8 66a8 8 0 0 0 3.2 15.34a7.9 7.9 0 0 0 3.2-.68A88 88 0 0 0 160 40"/></g></svg>
          </span>
          <span className={styles.label}>{LABEL}</span>
          <span className={styles.badge} style={badgeVars} aria-hidden="true">{BADGE_PREFIX} <b className={styles.n}></b></span>
        </div>
        <div className={styles.bar}>
          <span className={styles.meta}>{META}</span>
        </div>
      </div>
    </main>
  );
}