06CTA band — a strip whose border-angle value keeps increasing once it enters view

<main class="stage" id="stage">
  <section class="band">
    <p class="band__text">Start for free today</p>
    <div class="band__cta-wrap">
      <div class="band__ring" aria-hidden="true"></div>
      <button class="band__cta" type="button">Start free trial</button>
    </div>
  </section>
</main>

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

$duration: $dur-loop;
$easing: linear;
$color: $subject-ink;

@include stage($stage-yellow);

@property --angle {
  syntax: "<angle>";
  inherits: false;
  initial-value: 0deg;
}

.band {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-6;
  text-align: center;
}

.band__text {
  margin: 0;
  color: $color;
  font-weight: 700;
  font-size: clamp(16px, 5vmin, 22px);
  line-height: 1.35;
}

.band__cta-wrap {
  position: relative;
  padding: 4px;
  border-radius: $r-pill;
}

.band__ring {
  position: absolute;
  inset: 0;
  border-radius: $r-pill;
  background: conic-gradient(from var(--angle), $color, transparent 32%, $color);
  animation: spin $duration $easing infinite;
}

.band__cta {
  position: relative;
  border: 0;
  border-radius: calc(#{$r-pill} - 4px);
  padding: $sp-3 $sp-8;
  font-family: inherit;
  font-weight: 600;
  font-size: 13px;
  line-height: 1;
  color: $stage-yellow;
  background: $color;
  cursor: pointer;
}

@keyframes spin {
  to { --angle: 360deg; }
}

@media (max-width: 340px) {
  .band__cta { padding: $sp-2 $sp-6; }
}

@media (prefers-reduced-motion: reduce) {
  .band__ring { animation: none; }
}

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);
}

@property --angle {
  syntax: "<angle>";
  inherits: false;
  initial-value: 0deg;
}
.band {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 24px;
  text-align: center;
}

.band__text {
  margin: 0;
  color: #17141a;
  font-weight: 700;
  font-size: clamp(16px, 5vmin, 22px);
  line-height: 1.35;
}

.band__cta-wrap {
  position: relative;
  padding: 4px;
  border-radius: 999px;
}

.band__ring {
  position: absolute;
  inset: 0;
  border-radius: 999px;
  background: conic-gradient(from var(--angle), #17141a, transparent 32%, #17141a);
  animation: spin 2s linear infinite;
}

.band__cta {
  position: relative;
  border: 0;
  border-radius: calc(999px - 4px);
  padding: 12px 32px;
  font-family: inherit;
  font-weight: 600;
  font-size: 13px;
  line-height: 1;
  color: #ffd23f;
  background: #17141a;
  cursor: pointer;
}

@keyframes spin {
  to {
    --angle: 360deg;
  }
}
@media (max-width: 340px) {
  .band__cta {
    padding: 8px 24px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .band__ring {
    animation: none;
  }
}

import styles from "./CtaBand.module.scss";

// 회전하는 테두리의 각도 값(--angle)이 계속 늘어나며 conic-gradient 시작점을 돌린다.
// 계산 겹: 각도 값(--angle) -> conic-gradient 시작점 보간. 리스너 없음(자동 재생).
export default function CtaBand() {
  return (
    <main className={styles.stage}>
      <section className={styles.band}>
        <p className={styles.band__text}>지금 무료로 시작해보세요</p>
        <div className={styles["band__cta-wrap"]}>
          <div className={styles.band__ring} aria-hidden="true" />
          <button className={styles.band__cta} type="button">
            무료 체험 시작
          </button>
        </div>
      </section>
    </main>
  );
}