06Horizontal scroll-snap tabs

<main class="stage">
  <div class="st is-demo">
    <input type="radio" name="st-tab" id="st-1" class="st__radio" checked>
    <input type="radio" name="st-tab" id="st-2" class="st__radio">
    <input type="radio" name="st-tab" id="st-3" class="st__radio">
    <input type="radio" name="st-tab" id="st-4" class="st__radio">
    <input type="radio" name="st-tab" id="st-5" class="st__radio">
    <div class="st__scroller">
      <div class="st__nav">
        <label class="st__tab" for="st-1">All</label>
        <label class="st__tab" for="st-2">Clothing</label>
        <label class="st__tab" for="st-3">Shoes</label>
        <label class="st__tab" for="st-4">Bags</label>
        <label class="st__tab" for="st-5">Accessories</label>
        <span class="st__trail" aria-hidden="true"></span>
        <span class="st__indicator" aria-hidden="true"></span>
      </div>
    </div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-base;                             // 인디케이터가 미끄러지는 시간
$easing: $ease-lerp-settle;                       // 관성 lerp — 목표를 12.6% 넘겼다가 정착 (2026-09-15 형태 2차 한 겹)
$color: $subject-ink;                             // 인디케이터 색 (노란 무대라 어둡게)

@include stage($stage-yellow);

$tab-w: 88px;   // 탭 다섯 개가 같은 폭이라 인디케이터 이동값을 고정 배수로 쓸 수 있다

.st { width: min(260px, 78vw); }
.st__radio { position: absolute; opacity: 0; pointer-events: none; }

// 다섯 탭(88px × 5 = 440px)이 상자(260px)보다 넓어 가로로 넘친다 — 그래서 스냅 스크롤이 필요하다
.st__scroller {
  overflow-x: auto;
  overflow-y: hidden;
  scroll-snap-type: x mandatory;
  border-radius: $r-sm;
  -webkit-overflow-scrolling: touch;
}
.st__nav {
  position: relative;
  display: flex;
}
// 글자색·굵기는 항상 고정한다 — 밑줄(인디케이터)이 데모 루프에서 :checked 와 다른 탭에 가 있어도
// "이 탭이 진짜 활성" 이라는 잘못된 신호를 안 준다. 활성 신호는 밑줄 위치 하나로만 준다
.st__tab {
  flex: 0 0 $tab-w;
  scroll-snap-align: start;
  text-align: center;
  padding: $sp-3 $sp-1;
  font-weight: 600;
  font-size: clamp(12px, 3.4vw, 13px);
  line-height: 1;
  font-family: inherit;
  color: $subject-ink;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
}
.st__indicator {
  position: absolute; left: 0; bottom: 0;
  width: $tab-w; height: 3px;
  background: $color;
  border-radius: $r-pill;
  transform: translateX(0);
  transition: transform $duration $easing;
}
// 이동 궤적 트레일 잔상 — 인디케이터와 같은 .st__scroller 안(.st__nav 자식, .st__indicator 형제)에 둬야 st-scroll 로 같이 밀린다
.st__trail {
  position: absolute; left: 0; bottom: 0;
  width: $tab-w; height: 3px;
  background: $color;
  border-radius: $r-pill;
  opacity: .32;
  filter: blur(1.5px);
  transform: translateX(0);
  transition: transform calc($duration * 1.8) ease-out;
}

// ── 실제 동작: :checked 만으로 인디케이터가 옮겨간다 ──────────────
@for $i from 1 through 5 {
  #st-#{$i}:checked ~ .st__scroller .st__indicator { transform: translateX(#{$tab-w * ($i - 1)}); }
  #st-#{$i}:checked ~ .st__scroller .st__trail { transform: translateX(#{$tab-w * ($i - 1)}); }
}

// ── 데모 루프: 다섯 탭을 다 돈다. 상자(260px)엔 세 탭만 들어가므로
// 뒤 두 탭(가방·액세서리)로 갈 땐 .st__nav 자체를 밀어야 "스크롤"이 보인다 —
// 인디케이터만 옮기면 보이지도 않는 탭으로 움직여 아무 일도 안 일어나는 것처럼 보였다
// (사용자 2026-09-10 스크린샷 지적: 06 이 그냥 밑줄 3개 + 빈 공간으로 보임)
.st.is-demo .st__indicator { animation: st-loop $dur-loop $easing infinite; }
.st.is-demo .st__trail { animation: st-loop $dur-loop $easing infinite; animation-delay: calc($dur-loop * .06); } // 6% 위상만큼 늦게 쫓아가 트레일로 읽힌다
.st.is-demo .st__nav { animation: st-scroll $dur-loop $easing infinite; }
@keyframes st-loop {
  0%, 12%  { transform: translateX(0); }
  24%, 32% { transform: translateX(#{$tab-w}); }
  44%, 52% { transform: translateX(#{$tab-w * 2}); }
  64%, 72% { transform: translateX(#{$tab-w * 3}); }
  84%, 92% { transform: translateX(#{$tab-w * 4}); }
  100%     { transform: translateX(0); }
}
// 나머지 탭이 상자 안에 보이도록 탭 스트립 자체를 왼쪽으로 민다 (translateX — scrollLeft 는 WAAPI 로 못 잰다)
@keyframes st-scroll {
  0%, 12%, 24%, 32% { transform: translateX(0); }
  44%, 52%          { transform: translateX(#{-$tab-w}); }
  64%, 92%          { transform: translateX(#{-$tab-w * 2}); }
  100%              { transform: translateX(0); }
}

@media (prefers-reduced-motion: reduce) {
  .st__indicator, .st__trail { transition: none; }
  .st.is-demo .st__indicator, .st.is-demo .st__trail, .st.is-demo .st__nav { animation: none !important; }
  .st__trail { opacity: 0; } // 관성·트레일 한 겹은 reduced-motion 에서 완전히 꺼진다
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.st {
  width: min(260px, 78vw);
}

.st__radio {
  position: absolute;
  opacity: 0;
  pointer-events: none;
}

.st__scroller {
  overflow-x: auto;
  overflow-y: hidden;
  scroll-snap-type: x mandatory;
  border-radius: 8px;
  -webkit-overflow-scrolling: touch;
}

.st__nav {
  position: relative;
  display: flex;
}

.st__tab {
  flex: 0 0 88px;
  scroll-snap-align: start;
  text-align: center;
  padding: 12px 4px;
  font-weight: 600;
  font-size: clamp(12px, 3.4vw, 13px);
  line-height: 1;
  font-family: inherit;
  color: #17141a;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
}

.st__indicator {
  position: absolute;
  left: 0;
  bottom: 0;
  width: 88px;
  height: 3px;
  background: #17141a;
  border-radius: 999px;
  transform: translateX(0);
  transition: transform 300ms linear(0, 0.051, 0.176, 0.341, 0.518, 0.685, 0.831, 0.947, 1.032, 1.087, 1.117, 1.126, 1.121, 1.105, 1.085, 1.062, 1.041, 1.022, 1.008, 0.997, 1);
}

.st__trail {
  position: absolute;
  left: 0;
  bottom: 0;
  width: 88px;
  height: 3px;
  background: #17141a;
  border-radius: 999px;
  opacity: 0.32;
  filter: blur(1.5px);
  transform: translateX(0);
  transition: transform 540ms ease-out;
}

#st-1:checked ~ .st__scroller .st__indicator {
  transform: translateX(0px);
}

#st-1:checked ~ .st__scroller .st__trail {
  transform: translateX(0px);
}

#st-2:checked ~ .st__scroller .st__indicator {
  transform: translateX(88px);
}

#st-2:checked ~ .st__scroller .st__trail {
  transform: translateX(88px);
}

#st-3:checked ~ .st__scroller .st__indicator {
  transform: translateX(176px);
}

#st-3:checked ~ .st__scroller .st__trail {
  transform: translateX(176px);
}

#st-4:checked ~ .st__scroller .st__indicator {
  transform: translateX(264px);
}

#st-4:checked ~ .st__scroller .st__trail {
  transform: translateX(264px);
}

#st-5:checked ~ .st__scroller .st__indicator {
  transform: translateX(352px);
}

#st-5:checked ~ .st__scroller .st__trail {
  transform: translateX(352px);
}

.st.is-demo .st__indicator {
  animation: st-loop 2s linear(0, 0.051, 0.176, 0.341, 0.518, 0.685, 0.831, 0.947, 1.032, 1.087, 1.117, 1.126, 1.121, 1.105, 1.085, 1.062, 1.041, 1.022, 1.008, 0.997, 1) infinite;
}

.st.is-demo .st__trail {
  animation: st-loop 2s linear(0, 0.051, 0.176, 0.341, 0.518, 0.685, 0.831, 0.947, 1.032, 1.087, 1.117, 1.126, 1.121, 1.105, 1.085, 1.062, 1.041, 1.022, 1.008, 0.997, 1) infinite;
  animation-delay: 0.12s;
}

.st.is-demo .st__nav {
  animation: st-scroll 2s linear(0, 0.051, 0.176, 0.341, 0.518, 0.685, 0.831, 0.947, 1.032, 1.087, 1.117, 1.126, 1.121, 1.105, 1.085, 1.062, 1.041, 1.022, 1.008, 0.997, 1) infinite;
}

@keyframes st-loop {
  0%, 12% {
    transform: translateX(0);
  }
  24%, 32% {
    transform: translateX(88px);
  }
  44%, 52% {
    transform: translateX(176px);
  }
  64%, 72% {
    transform: translateX(264px);
  }
  84%, 92% {
    transform: translateX(352px);
  }
  100% {
    transform: translateX(0);
  }
}
@keyframes st-scroll {
  0%, 12%, 24%, 32% {
    transform: translateX(0);
  }
  44%, 52% {
    transform: translateX(-88px);
  }
  64%, 92% {
    transform: translateX(-176px);
  }
  100% {
    transform: translateX(0);
  }
}
@media (prefers-reduced-motion: reduce) {
  .st__indicator, .st__trail {
    transition: none;
  }
  .st.is-demo .st__indicator, .st.is-demo .st__trail, .st.is-demo .st__nav {
    animation: none !important;
  }
  .st__trail {
    opacity: 0;
  }
}

// 스크롤은 브라우저 scroll-snap 이 처리한다. 이동은 :checked 만으로 동작. 실제 클릭이면 데모 루프만 뗀다.
document.querySelectorAll('.st__radio').forEach(function (r) {
  r.addEventListener('pointerdown', function () { document.querySelector('.st').classList.remove('is-demo'); });
});

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

const TABS = ["전체", "의류", "신발", "가방", "액세서리"];
const TAB_W = 88;

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

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

export default function ScrollTabs({ duration = 300, easing = "cubic-bezier(.2,.8,.2,1)", color = "#17141a" }: ScrollTabsProps) {
  const [active, setActive] = useState(0);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color, "--i": active };

  return (
    <div className={styles.st} style={vars}>
      <div className={styles.scroller}>
        <div className={styles.nav} role="tablist">
          {TABS.map((t, i) => (
            <button key={t} type="button" role="tab" aria-selected={i === active}
                    className={styles.tab} style={{ flex: `0 0 ${TAB_W}px` }} onClick={() => setActive(i)}>
              {t}
            </button>
          ))}
          <span className={styles.indicator} aria-hidden="true" />
        </div>
      </div>
    </div>
  );
}