04太くなる下線

<main class="stage">
  <a class="link is-demo" href="#">今読んでいる記事</a>
</main>

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

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

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

.link {
  color: $subject-ink;
  text-decoration-line: underline;
  text-decoration-style: solid;   // wavy 가 아니라 solid — 046-04 는 물결, 이 항목은 굵기만 바뀐다
  text-decoration-color: $color;
  text-decoration-thickness: 1px;
  text-underline-offset: 3px;
  font-weight: 700; font-size: clamp(18px, 5vw, 26px); line-height: 1.4;
  transition: text-decoration-thickness $duration $easing, text-underline-offset $duration $easing;
}
.link:hover, .link:focus-visible {
  text-decoration-thickness: 4px;
  text-underline-offset: 5px;
}
.link.is-demo {
  animation: underline-thick $dur-loop $easing infinite;
}

@keyframes underline-thick {
  0%, 100%  { text-decoration-thickness: 1px; text-underline-offset: 3px; }
  35%, 60%  { text-decoration-thickness: 4px; text-underline-offset: 5px; }
}

@media (prefers-reduced-motion: reduce) {
  .link, .link.is-demo { transition: none; animation: none; }
  .link:hover, .link:focus-visible { text-decoration-thickness: 4px; text-underline-offset: 5px; }
}

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);
}

.link {
  color: #17141a;
  text-decoration-line: underline;
  text-decoration-style: solid;
  text-decoration-color: #2f6df6;
  text-decoration-thickness: 1px;
  text-underline-offset: 3px;
  font-weight: 700;
  font-size: clamp(18px, 5vw, 26px);
  line-height: 1.4;
  transition: text-decoration-thickness 300ms ease-out, text-underline-offset 300ms ease-out;
}

.link:hover, .link:focus-visible {
  text-decoration-thickness: 4px;
  text-underline-offset: 5px;
}

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

@keyframes underline-thick {
  0%, 100% {
    text-decoration-thickness: 1px;
    text-underline-offset: 3px;
  }
  35%, 60% {
    text-decoration-thickness: 4px;
    text-underline-offset: 5px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .link, .link.is-demo {
    transition: none;
    animation: none;
  }
  .link:hover, .link:focus-visible {
    text-decoration-thickness: 4px;
    text-underline-offset: 5px;
  }
}

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 "./ThickGrowUnderline.module.scss";

export type ThickGrowUnderlineProps = { children: ReactNode; href: string; duration?: number; color?: string; maxThickness?: number };

export default function ThickGrowUnderline({ children, href, duration = 300, color = "#2f6df6", maxThickness = 4 }: ThickGrowUnderlineProps) {
  const vars = { "--duration": `${duration}ms`, "--color": color, "--max-thickness": `${maxThickness}px` } as CSSProperties;
  return (
    <a className={styles.link} href={href} style={vars}>
      {children}
    </a>
  );
}