08Vạch chỉ báo tab trượt

<main class="stage">
  <nav class="tabs is-demo" role="tablist">
    <button class="tabs__item is-active" type="button" role="tab" aria-selected="true">Tổng quan</button>
    <button class="tabs__item" type="button" role="tab" aria-selected="false">Cài đặt</button>
    <button class="tabs__item" type="button" role="tab" aria-selected="false">Thanh toán</button>
    <span class="tabs__indicator" aria-hidden="true"></span>
  </nav>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-base;                               // 인디케이터가 옮겨가는 시간
$easing: $ease-spring;                               // 이동 곡선
$color: $subject-blue;                               // 인디케이터·활성 탭 색

// ── 데모 무대 ──────────────────────────────────────────
@include stage($stage-paper);

.tabs {
  position: relative;
  display: grid;
  grid-template-columns: repeat(3, 1fr);             // 세 칸을 똑같은 폭으로 — 그래야 translateX 배수만으로 옮겨간다
  width: min(240px, 84vw);
  background: $subject-cream;
  border-radius: $r-control;
  padding: 4px;
  --i: 0;                                            // 실제 클릭이 여기에 인덱스를 써 넣는다

  &__item {
    position: relative;
    z-index: 1;
    border: 0;
    background: transparent;
    padding: clamp(9px, 3vw, 12px) 4px;
    font-weight: 700;
    font-size: clamp(12px, 3.4vw, 14px);
    line-height: 1;
    font-family: inherit;
    color: rgba($stage-ink, .72);                    // 흐린 글자는 알파가 아니라 색으로 — .72 가 크림 면 위 6.9:1
    cursor: pointer;

    &.is-active { color: $subject-blue-deep; }       // 색은 상태값 — 트랜지션 없이 즉시. 크림 면 위 파란 글자는 deep(5.98:1)
  }

  &__indicator {
    position: absolute;
    left: 4px; bottom: 4px;
    width: calc((100% - 8px) / 3);
    height: 3px;
    border-radius: $r-pill;
    background: $color;
    transform: translateX(calc(var(--i, 0) * 100%));
    transition: transform $duration $easing;
  }

  &.is-demo &__indicator { animation: tab-loop $dur-loop $easing infinite; }
}

@keyframes tab-loop {
  0%, 20%  { transform: translateX(0%); }
  33%, 53% { transform: translateX(100%); }
  66%, 86% { transform: translateX(200%); }
  100%     { transform: translateX(0%); }
}

// ── 접근성: 움직임 줄이기 설정이면 즉시 전환, 첫 탭에 고정 ────────
@media (prefers-reduced-motion: reduce) {
  .tabs__indicator { transition: none; }
  .tabs.is-demo .tabs__indicator { animation: none !important; }
}

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);
}

.tabs {
  position: relative;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  width: min(240px, 84vw);
  background: #fff7e6;
  border-radius: 12px;
  padding: 4px;
  --i: 0;
}
.tabs__item {
  position: relative;
  z-index: 1;
  border: 0;
  background: transparent;
  padding: clamp(9px, 3vw, 12px) 4px;
  font-weight: 700;
  font-size: clamp(12px, 3.4vw, 14px);
  line-height: 1;
  font-family: inherit;
  color: rgba(23, 20, 26, 0.72);
  cursor: pointer;
}
.tabs__item.is-active {
  color: #0a4fe8;
}
.tabs__indicator {
  position: absolute;
  left: 4px;
  bottom: 4px;
  width: calc((100% - 8px) / 3);
  height: 3px;
  border-radius: 999px;
  background: #2f6df6;
  transform: translateX(calc(var(--i, 0) * 100%));
  transition: transform 300ms cubic-bezier(0.2, 0.8, 0.2, 1);
}
.tabs.is-demo .tabs__indicator {
  animation: tab-loop 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

@keyframes tab-loop {
  0%, 20% {
    transform: translateX(0%);
  }
  33%, 53% {
    transform: translateX(100%);
  }
  66%, 86% {
    transform: translateX(200%);
  }
  100% {
    transform: translateX(0%);
  }
}
@media (prefers-reduced-motion: reduce) {
  .tabs__indicator {
    transition: none;
  }
  .tabs.is-demo .tabs__indicator {
    animation: none !important;
  }
}

// 실제 클릭: 누른 탭으로 인디케이터가 옮겨간다. 데모(.is-demo) 루프는 클릭하면 멈춘다.
var tabs = document.querySelectorAll('.tabs__item');
var nav = document.querySelector('.tabs');
tabs.forEach(function (t, i) {
  t.addEventListener('click', function () {
    nav.classList.remove('is-demo');
    tabs.forEach(function (x) { x.classList.remove('is-active'); x.setAttribute('aria-selected', 'false'); });
    t.classList.add('is-active');
    t.setAttribute('aria-selected', 'true');
    nav.style.setProperty('--i', i);
  });
});

import { useState } from "react";
import type { CSSProperties } from "react";
import styles from "./TabIndicatorSlide.module.scss";

export type TabIndicatorSlideProps = {
  tabs: string[];
  /** 인디케이터가 옮겨가는 시간 (기본 300ms) */
  duration?: number;
  easing?: string;
  color?: string;
};

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

export default function TabIndicatorSlide({
  tabs,
  duration = 300,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#2f6df6",
}: TabIndicatorSlideProps) {
  const [active, setActive] = useState(0);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--i": active };

  return (
    <nav className={styles.tabs} role="tablist" style={{ ...vars, ["--color" as string]: color }}>
      {tabs.map((label, i) => (
        <button
          key={label}
          type="button"
          role="tab"
          aria-selected={i === active}
          className={i === active ? `${styles.item} ${styles.active}` : styles.item}
          onClick={() => setActive(i)}
        >
          {label}
        </button>
      ))}
      <span className={styles.indicator} style={{ width: `calc((100% - 8px) / ${tabs.length})` }} aria-hidden="true" />
    </nav>
  );
}