06CTA underline sweep (parent hover)

<main class="stage">
  <article class="card is-demo" tabindex="0">
    <div class="card__body">
      <h3 class="card__title">Brand story</h3>
      <p class="card__meta">Why we make it</p>
      <span class="cta">
        <span class="cta__label">Learn more</span>
        <span class="cta__underline" aria-hidden="true"></span>
      </span>
    </div>
  </article>
</main>

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

$duration: $dur-base;                                   // 밑줄이 그려지는 시간
$easing: $ease-out;
$color: $subject-blue;                                    // CTA 색

@include stage($stage-yellow);
.stage { padding: clamp(8px, 2.4vw, 16px); }

.card {
  width: min(160px, 50vw);
  border-radius: $r-card;
  background: $stage-paper;
  box-shadow: $shadow-press;
  padding: $sp-3;
  box-sizing: border-box;
  outline: none;
  cursor: pointer;
}
.card__title { margin: 0 0 $sp-1; font-weight: 700; font-size: clamp(12px, 3.4vw, 14px); line-height: 1.3; font-family: inherit; color: $stage-ink; }
.card__meta { margin: 0; font-weight: 500; font-size: clamp(11px, 3vw, 12px); line-height: 1.3; font-family: inherit; color: rgba($stage-ink, .6); }
.cta {
  position: relative;
  display: inline-block;
  margin-top: $sp-2;
  font-weight: 700; font-size: 12px; line-height: 1.3; font-family: inherit;
  color: $color;
}
.cta__underline {
  position: absolute;
  left: 0; right: 0; bottom: -2px;
  height: 2px;
  background: $color;
  transform: scaleX(0);
  transform-origin: left; // 규칙8: 좌변서 그어짐
  transition: transform $duration $easing;
}

// 밑줄 자체가 아니라 카드 어디에 올려도 부모 :hover 가 자식 밑줄을 켠다
.card:hover .cta__underline,
.card:focus-visible .cta__underline,
.card:active .cta__underline {
  transform: scaleX(1);
}
.card.is-demo .cta__underline { animation: underline-loop $dur-loop $easing infinite; }
@keyframes underline-loop {
  0%, 15%  { transform: scaleX(0); }
  45%, 75% { transform: scaleX(1); }
  100%     { transform: scaleX(0); }
}

@media (prefers-reduced-motion: reduce) {
  .cta__underline { transition: none; }
  .card.is-demo .cta__underline { animation: none; transform: scaleX(1); }
}

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);
}

.stage {
  padding: clamp(8px, 2.4vw, 16px);
}

.card {
  width: min(160px, 50vw);
  border-radius: 16px;
  background: #ffffff;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  padding: 12px;
  box-sizing: border-box;
  outline: none;
  cursor: pointer;
}

.card__title {
  margin: 0 0 4px;
  font-weight: 700;
  font-size: clamp(12px, 3.4vw, 14px);
  line-height: 1.3;
  font-family: inherit;
  color: #17141a;
}

.card__meta {
  margin: 0;
  font-weight: 500;
  font-size: clamp(11px, 3vw, 12px);
  line-height: 1.3;
  font-family: inherit;
  color: rgba(23, 20, 26, 0.6);
}

.cta {
  position: relative;
  display: inline-block;
  margin-top: 8px;
  font-weight: 700;
  font-size: 12px;
  line-height: 1.3;
  font-family: inherit;
  color: #2f6df6;
}

.cta__underline {
  position: absolute;
  left: 0;
  right: 0;
  bottom: -2px;
  height: 2px;
  background: #2f6df6;
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 300ms ease-out;
}

.card:hover .cta__underline,
.card:focus-visible .cta__underline,
.card:active .cta__underline {
  transform: scaleX(1);
}

.card.is-demo .cta__underline {
  animation: underline-loop 2s ease-out infinite;
}

@keyframes underline-loop {
  0%, 15% {
    transform: scaleX(0);
  }
  45%, 75% {
    transform: scaleX(1);
  }
  100% {
    transform: scaleX(0);
  }
}
@media (prefers-reduced-motion: reduce) {
  .cta__underline {
    transition: none;
  }
  .card.is-demo .cta__underline {
    animation: none;
    transform: scaleX(1);
  }
}

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

export type CtaUnderlineCardProps = {
  title: string;
  meta: string;
  cta: string;
  /** 밑줄이 그려지는 시간 (기본 300ms) */
  duration?: number;
  easing?: string;
  /** CTA 색 */
  color?: string;
};

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

/** 밑줄 자체가 아니라 카드 어디에 올려도 부모 :hover 가 자식 밑줄을 켠다 */
export default function CtaUnderlineCard({
  title,
  meta,
  cta,
  duration = 300,
  easing = "ease-out",
  color = "#2f6df6",
}: CtaUnderlineCardProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  return (
    <article className={styles.card} style={vars} tabIndex={0}>
      <h3 className={styles.title}>{title}</h3>
      <p className={styles.meta}>{meta}</p>
      <span className={styles.cta}>
        <span>{cta}</span>
        <span className={styles.underline} aria-hidden="true" />
      </span>
    </article>
  );
}