03Multi-line underline

<main class="stage">
  <p class="wrap"><a class="link is-demo" href="#">See all notices again</a></p>
</main>

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

// ── 변수 3개 ─────────────────────────────
$duration: $dur-base;
$easing:   $ease-out;
$color:    $subject-cream;

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

// box-decoration-break: clone 이 인라인 흐름에서만 줄마다 적용되므로 부모 폭을 좁혀 두 줄로 감싼다
.wrap {
  margin: 0;
  width: 160px;   // max-width 는 그리드 place-items:center 아래서 내용 폭에 clamp 되지 않고 그대로 넓어졌다(실측) — 고정 width 로 강제로 줄바꿈시킨다
  text-align: center;
}

.link {
  color: $color;
  text-decoration: none;
  font-weight: 700; font-size: clamp(16px, 4.4vw, 20px); line-height: 1.6;

  // 밑줄을 border/의사요소가 아니라 background-image 로 그린다 — box-decoration-break: clone 이
  // 줄마다(fragment마다) 이 배경을 통째로 복제해 각 줄의 밑줄을 독립적으로 그린다.
  // repeat-x 를 쓰면 크기가 작아도 타일이 반복돼 처음부터 꽉 차 보인다(실측 — 렌더 측정에서 움직인 프레임 1/23) → no-repeat
  background-image: linear-gradient(currentColor, currentColor);
  background-repeat: no-repeat;
  background-position: 0 100%;
  background-size: 0% 2px;
  box-decoration-break: clone;
  -webkit-box-decoration-break: clone;
  transition: background-size $duration $easing;
}
.link:hover, .link:focus-visible {
  background-size: 100% 2px;
}
.link.is-demo {
  animation: underline-multiline $dur-loop $easing infinite;
}

@keyframes underline-multiline {
  0%, 100%  { background-size: 0% 2px; }
  35%, 60%  { background-size: 100% 2px; }
}

@media (prefers-reduced-motion: reduce) {
  .link, .link.is-demo { transition: none; animation: none; }
  .link:hover, .link:focus-visible { background-size: 100% 2px; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.wrap {
  margin: 0;
  width: 160px;
  text-align: center;
}

.link {
  color: #fff7e6;
  text-decoration: none;
  font-weight: 700;
  font-size: clamp(16px, 4.4vw, 20px);
  line-height: 1.6;
  background-image: linear-gradient(currentColor, currentColor);
  background-repeat: no-repeat;
  background-position: 0 100%;
  background-size: 0% 2px;
  box-decoration-break: clone;
  -webkit-box-decoration-break: clone;
  transition: background-size 300ms ease-out;
}

.link:hover, .link:focus-visible {
  background-size: 100% 2px;
}

.link.is-demo {
  animation: underline-multiline 2s ease-out infinite;
}

@keyframes underline-multiline {
  0%, 100% {
    background-size: 0% 2px;
  }
  35%, 60% {
    background-size: 100% 2px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .link, .link.is-demo {
    transition: none;
    animation: none;
  }
  .link:hover, .link:focus-visible {
    background-size: 100% 2px;
  }
}

document.querySelectorAll('.link').forEach(function (b) {
  b.addEventListener('pointerenter', function () { b.classList.remove('is-demo'); });
  b.addEventListener('click', function (e) { e.preventDefault(); });
});

import type { CSSProperties, ReactNode } from "react";
import styles from "./MultilineUnderline.module.scss";

export type MultilineUnderlineProps = { children: ReactNode; href: string; duration?: number; color?: string; maxWidth?: number };

export default function MultilineUnderline({ children, href, duration = 300, color = "currentColor", maxWidth = 160 }: MultilineUnderlineProps) {
  const vars = { "--duration": `${duration}ms`, "--color": color, "--max-width": `${maxWidth}px` } as CSSProperties;
  return (
    <p className={styles.wrap} style={vars}>
      <a className={styles.link} href={href}>
        {children}
      </a>
    </p>
  );
}