06Đổi giá bằng :has(:checked), 0 JS

<main class="stage">
  <div class="hc-card is-demo">
    <div class="hc-toggle">
      <input type="radio" name="hc-period" id="hc-monthly" class="hc-radio hc-radio--m" checked>
      <input type="radio" name="hc-period" id="hc-yearly" class="hc-radio hc-radio--y">
      <label for="hc-monthly">Monthly</label>
      <label for="hc-yearly">Yearly</label>
    </div>
    <div class="hc-price-stack">
      <div class="hc-price hc-price--monthly">$29<span>/mo</span></div>
      <div class="hc-price hc-price--yearly">$19<span>/mo</span></div>
    </div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-base;
$easing: $ease-out;
$color: $subject-blue-deep;   // 크림 글자가 얹히므로 진한 파랑

@include stage($stage-yellow);

.hc-card {
  width: min(220px, 80vw);
  box-sizing: border-box;
  border-radius: $r-card;
  padding: $sp-5;
  background: $subject-ink;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-4;
}

.hc-toggle {
  display: flex;
  gap: $sp-2;
}
.hc-radio { position: absolute; opacity: 0; pointer-events: none; }
.hc-toggle label {
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  cursor: pointer;
  color: $subject-cream;
  background: rgba(255, 255, 255, .08);
  font: 600 11px/1 -apple-system, "Segoe UI", sans-serif;
  transition: background $duration $easing;
}
// 순수 CSS: 숨긴 라디오의 :checked 상태를 :has() 로 읽어 카드 전체에서 판단한다 (JS 0)
.hc-card:has(.hc-radio--m:checked) label[for="hc-monthly"],
.hc-card:has(.hc-radio--y:checked) label[for="hc-yearly"] {
  background: $color;
}

.hc-price-stack { position: relative; width: 100%; height: 44px; }
.hc-price {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: baseline;
  justify-content: center;
  gap: $sp-1;
  color: $subject-cream;
  font: 700 26px/1 -apple-system, "Segoe UI", sans-serif;
  opacity: 0;
  transform: translateY($sp-2);
  transition: opacity $duration $easing, transform $duration $easing;
}
.hc-price span { font-size: 12px; font-weight: 500; opacity: .6; }
.hc-price--monthly { opacity: 1; transform: none; }
.hc-card:has(.hc-radio--y:checked) .hc-price--monthly { opacity: 0; transform: translateY(-#{$sp-2}); }
.hc-card:has(.hc-radio--y:checked) .hc-price--yearly { opacity: 1; transform: none; }

// 데모 루프: 헤드리스는 :has(:checked) 를 못 걸어 is-demo 가 같은 크로스페이드를 keyframes 로 반복한다
@keyframes hc-cross-a {
  0%, 40% { opacity: 1; transform: none; }
  50%, 90% { opacity: 0; transform: translateY(-#{$sp-2}); }
  100% { opacity: 1; transform: none; }
}
@keyframes hc-cross-b {
  0%, 40% { opacity: 0; transform: translateY($sp-2); }
  50%, 90% { opacity: 1; transform: none; }
  100% { opacity: 0; transform: translateY($sp-2); }
}
.hc-card.is-demo .hc-price--monthly { animation: hc-cross-a $duration * 4 $easing infinite; }
.hc-card.is-demo .hc-price--yearly { animation: hc-cross-b $duration * 4 $easing infinite; }

@media (prefers-reduced-motion: reduce) {
  .hc-price,
  .hc-card.is-demo .hc-price { animation: none !important; transition: none !important; }
}

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);
}

.hc-card {
  width: min(220px, 80vw);
  box-sizing: border-box;
  border-radius: 16px;
  padding: 20px;
  background: #17141a;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
}

.hc-toggle {
  display: flex;
  gap: 8px;
}

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

.hc-toggle label {
  padding: 4px 12px;
  border-radius: 999px;
  cursor: pointer;
  color: #fff7e6;
  background: rgba(255, 255, 255, 0.08);
  font: 600 11px/1 -apple-system, "Segoe UI", sans-serif;
  transition: background 300ms ease-out;
}

.hc-card:has(.hc-radio--m:checked) label[for=hc-monthly],
.hc-card:has(.hc-radio--y:checked) label[for=hc-yearly] {
  background: #0a4fe8;
}

.hc-price-stack {
  position: relative;
  width: 100%;
  height: 44px;
}

.hc-price {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: baseline;
  justify-content: center;
  gap: 4px;
  color: #fff7e6;
  font: 700 26px/1 -apple-system, "Segoe UI", sans-serif;
  opacity: 0;
  transform: translateY(8px);
  transition: opacity 300ms ease-out, transform 300ms ease-out;
}

.hc-price span {
  font-size: 12px;
  font-weight: 500;
  opacity: 0.6;
}

.hc-price--monthly {
  opacity: 1;
  transform: none;
}

.hc-card:has(.hc-radio--y:checked) .hc-price--monthly {
  opacity: 0;
  transform: translateY(-8px);
}

.hc-card:has(.hc-radio--y:checked) .hc-price--yearly {
  opacity: 1;
  transform: none;
}

@keyframes hc-cross-a {
  0%, 40% {
    opacity: 1;
    transform: none;
  }
  50%, 90% {
    opacity: 0;
    transform: translateY(-8px);
  }
  100% {
    opacity: 1;
    transform: none;
  }
}
@keyframes hc-cross-b {
  0%, 40% {
    opacity: 0;
    transform: translateY(8px);
  }
  50%, 90% {
    opacity: 1;
    transform: none;
  }
  100% {
    opacity: 0;
    transform: translateY(8px);
  }
}
.hc-card.is-demo .hc-price--monthly {
  animation: hc-cross-a 1200ms ease-out infinite;
}

.hc-card.is-demo .hc-price--yearly {
  animation: hc-cross-b 1200ms ease-out infinite;
}

@media (prefers-reduced-motion: reduce) {
  .hc-price,
  .hc-card.is-demo .hc-price {
    animation: none !important;
    transition: none !important;
  }
}

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

export interface PriceSwapHasCheckedProps {
  duration?: string;
  easing?: string;
  monthly?: string;
  yearly?: string;
  name?: string;
}

// 실사용: 숨긴 라디오 상태를 :has() 로 카드 전체에서 읽는다. 자바스크립트 0.
export default function PriceSwapHasChecked({
  duration = "300ms",
  easing = "ease-out",
  monthly = "$29",
  yearly = "$19",
  name = "hc-period",
}: PriceSwapHasCheckedProps) {
  const style = { "--duration": duration, "--easing": easing } as CSSProperties;

  return (
    <div className={styles.card} style={style}>
      <div className={styles.toggle}>
        <input type="radio" name={name} id={`${name}-m`} className={styles.radioM} defaultChecked />
        <input type="radio" name={name} id={`${name}-y`} className={styles.radioY} />
        <label htmlFor={`${name}-m`}>Monthly</label>
        <label htmlFor={`${name}-y`}>Yearly</label>
      </div>
      <div className={styles.stack}>
        <div className={`${styles.price} ${styles.priceMonthly}`}>{monthly}<span>/mo</span></div>
        <div className={`${styles.price} ${styles.priceYearly}`}>{yearly}<span>/mo</span></div>
      </div>
    </div>
  );
}