09Auto numbering via sibling-index()

<main class="stage">
  <ul class="ts09-list is-demo">
    <li class="ts09-step" aria-label="Step 1: Sign up">Sign up</li>
    <li class="ts09-step" aria-label="Step 2: Shipping">Shipping</li>
    <li class="ts09-step" aria-label="Step 3: Payment">Payment</li>
    <li class="ts09-step" aria-label="Step 4: Done">Done</li>
  </ul>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;
$easing: $ease-pop;
$color: $subject-blue;

@include stage($stage-ink);

.ts09-list {
  margin: 0;
  padding: 0;
  list-style: none;
  width: min(200px, 76vw);
  counter-reset: n 0;
}

.ts09-step {
  position: relative;
  display: flex;
  align-items: center;
  gap: $sp-3;
  padding: $sp-2 0 $sp-2 $sp-10;
  color: $subject-cream;
  font: 600 13px/1 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  opacity: 0;
  transform: scale(.7);

  // 기본(폴백): 순서대로 자동 증가하는 CSS 카운터
  counter-increment: n;
  &::before {
    content: counter(n);
    position: absolute;
    left: 0;
    width: 28px;
    height: 28px;
    border-radius: 50%;
    background: $color;
    color: $subject-cream;
    display: grid;
    place-items: center;
    font-weight: 700;
    font-size: 12px;
    line-height: 1;
    font-family: inherit;
  }
}

// 실제 사용 코드: sibling-index() 를 지원하면 순서가 바뀌어도(드래그 정렬) nth-child 없이 번호가 맞는다
@supports (z-index: calc(sibling-index())) {
  .ts09-step {
    counter-increment: none;
    counter-set: n calc(sibling-index());
    animation-delay: calc((sibling-index() - 1) * 120ms);
  }
}

.ts09-list.is-demo .ts09-step {
  animation: ts09-in $duration $easing infinite;
}

@keyframes ts09-in {
  0%   { opacity: 0; transform: scale(.7); }
  20%  { opacity: 1; transform: scale(1.08); }
  32%  { opacity: 1; transform: scale(1); }
  90%  { opacity: 1; transform: scale(1); }
  100% { opacity: 0; transform: scale(.7); }
}

@media (prefers-reduced-motion: reduce) {
  .ts09-step, .ts09-list.is-demo .ts09-step { animation: none !important; opacity: 1 !important; transform: none !important; }
}

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);
}

.ts09-list {
  margin: 0;
  padding: 0;
  list-style: none;
  width: min(200px, 76vw);
  counter-reset: n 0;
}

.ts09-step {
  position: relative;
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 8px 0 8px 40px;
  color: #fff7e6;
  font: 600 13px/1 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  opacity: 0;
  transform: scale(0.7);
  counter-increment: n;
}
.ts09-step::before {
  content: counter(n);
  position: absolute;
  left: 0;
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: #2f6df6;
  color: #fff7e6;
  display: grid;
  place-items: center;
  font-weight: 700;
  font-size: 12px;
  line-height: 1;
  font-family: inherit;
}

@supports (z-index: calc(sibling-index())) {
  .ts09-step {
    counter-increment: none;
    counter-set: n calc(sibling-index());
    animation-delay: calc((sibling-index() - 1) * 120ms);
  }
}
.ts09-list.is-demo .ts09-step {
  animation: ts09-in 2s cubic-bezier(0.2, 1.4, 0.4, 1) infinite;
}

@keyframes ts09-in {
  0% {
    opacity: 0;
    transform: scale(0.7);
  }
  20% {
    opacity: 1;
    transform: scale(1.08);
  }
  32% {
    opacity: 1;
    transform: scale(1);
  }
  90% {
    opacity: 1;
    transform: scale(1);
  }
  100% {
    opacity: 0;
    transform: scale(0.7);
  }
}
@media (prefers-reduced-motion: reduce) {
  .ts09-step, .ts09-list.is-demo .ts09-step {
    animation: none !important;
    opacity: 1 !important;
    transform: none !important;
  }
}

import { CSSProperties } from "react";
import styles from "./SiblingIndexNumbering.module.scss";

type Vars = CSSProperties & {
  "--duration"?: string;
  "--easing"?: string;
  "--color"?: string;
};

export interface SiblingIndexNumberingProps {
  duration?: string;
  easing?: string;
  color?: string;
  steps?: string[];
}

export default function SiblingIndexNumbering({
  duration = "2s",
  easing = "cubic-bezier(.2, 1.4, .4, 1)",
  color = "#2f6df6",
  steps = ["가입", "배송", "결제", "완료"],
}: SiblingIndexNumberingProps) {
  const style: Vars = { "--duration": duration, "--easing": easing, "--color": color };
  return (
    <ul className={styles.list} style={style}>
      {steps.map((s, i) => (
        <li key={s} className={styles.step} aria-label={`${i + 1}번째 단계: ${s}`}>{s}</li>
      ))}
    </ul>
  );
}