08Nút pill giãn khi hover

<main class="stage">
  <button type="button" class="totop" aria-label="Lên đầu trang">
    <svg class="totop__arrow" viewBox="0 0 24 24" aria-hidden="true"><polyline points="5,15 12,8 19,15"/></svg>
    <span class="totop__label">Lên đầu trang</span>
  </button>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: 220ms;
$easing: $ease-out;
$color: $subject-ink;      // 글자·화살표 색

@include stage($stage-paper);

.totop {
  display: inline-flex;
  align-items: center;
  gap: $sp-2;
  width: 48px;
  height: 48px;
  padding: 0 $sp-3;
  border: 0;
  border-radius: $r-pill;
  background: $stage-yellow;
  overflow: hidden;
  box-shadow: $shadow-raised;
  cursor: pointer;
  transition: width $duration $easing;
}
// 실제 사용: 마우스를 올리거나 포커스하면 폭이 넓어져 라벨이 드러난다
.totop:hover,
.totop:focus-visible,
.totop.is-demo-open { width: 132px; }

.totop__arrow {
  flex: none;
  width: 20px; height: 20px;
  fill: none;
  stroke: $color;
  stroke-width: 2.4;
  stroke-linecap: round;
  stroke-linejoin: round;
}
.totop__label {
  font: 600 clamp(13px, 3.6vw, 14px)/1 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  color: $color;
  white-space: nowrap;
}

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

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);
}

.totop {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  width: 48px;
  height: 48px;
  padding: 0 12px;
  border: 0;
  border-radius: 999px;
  background: #ffd23f;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  cursor: pointer;
  transition: width 220ms ease-out;
}

.totop:hover,
.totop:focus-visible,
.totop.is-demo-open {
  width: 132px;
}

.totop__arrow {
  flex: none;
  width: 20px;
  height: 20px;
  fill: none;
  stroke: #17141a;
  stroke-width: 2.4;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.totop__label {
  font: 600 clamp(13px, 3.6vw, 14px)/1 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  color: #17141a;
  white-space: nowrap;
}

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

// .is-demo 자동 재생: 진짜 :hover·:focus-visible 규칙을 그대로 타도록 is-demo-open 만 오간다.
// 500ms 간격 — 2초 측정 창 안에 전이(220ms)가 4번 들어가야 움직인 프레임 하한(6)에 여유가 생긴다
// (실측 2026-09-10: 1000ms 간격은 전이 2번뿐이라 5~6 프레임 경계에서 흔들렸다)
var btn = document.querySelector('.totop');
var t = function () { btn.classList.toggle('is-demo-open'); };
t(); setInterval(t, 500);

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

export type PillExpandButtonProps = {
  label?: string;
  /** 폭이 넓어지는 시간 (기본 220ms) */
  duration?: number;
  easing?: string;
};

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

// 실제 사용: 마우스를 올리거나 포커스하면 폭이 넓어져 라벨이 드러난다. 상태 없이 CSS 로 처리한다
export default function PillExpandButton({
  label = "맨 위로",
  duration = 220,
  easing = "ease-out",
}: PillExpandButtonProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing };
  return (
    <button
      type="button"
      className={styles.totop}
      style={vars}
      aria-label={label}
      onClick={() => window.scrollTo({ top: 0, behavior: "smooth" })}
    >
      <svg className={styles.arrow} viewBox="0 0 24 24" aria-hidden="true">
        <polyline points="5,15 12,8 19,15" />
      </svg>
      <span className={styles.label}>{label}</span>
    </button>
  );
}