08Rainbow border

<main class="stage">
  <span class="badge is-demo">Event</span>
</main>

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

$duration: $dur-loop;                                   // 색이 한 바퀴 도는 시간
$easing: linear;
$color: $stage-orange;                                  // (참고용, 실제 색은 아래 무지개 그라데이션)

@include stage($stage-paper);
.stage { padding: clamp(6px, 2.4vw, 16px); }

.badge {
  display: inline-block;
  border: 4px solid;
  border-image-slice: 1;
  // 토큰 4색으로 이은 그라데이션 — 팔레트 밖 hex 를 새로 쓰지 않는다 (blog-design)
  border-image-source: linear-gradient(90deg, $error, $stage-orange, $stage-yellow, $subject-blue, $error);
  border-radius: 4px;
  padding: 14px 22px;
  font-weight: 700; font-size: clamp(13px, 3.6vw, 15px); line-height: 1; font-family: inherit;
  color: $stage-ink;
  background: $stage-paper;
}
// 그라데이션 각도는 그대로 두고 filter: hue-rotate 만 돌려 색만 자리에서 순환시킨다
.badge.is-demo { animation: hue $duration $easing infinite; }
@keyframes hue { to { filter: hue-rotate(360deg); } }

@media (prefers-reduced-motion: reduce) {
  .badge.is-demo { animation: none; filter: none; }
}

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);
}

.stage {
  padding: clamp(6px, 2.4vw, 16px);
}

.badge {
  display: inline-block;
  border: 4px solid;
  border-image-slice: 1;
  border-image-source: linear-gradient(90deg, #c2361a, #ff4d1f, #ffd23f, #2f6df6, #c2361a);
  border-radius: 4px;
  padding: 14px 22px;
  font-weight: 700;
  font-size: clamp(13px, 3.6vw, 15px);
  line-height: 1;
  font-family: inherit;
  color: #17141a;
  background: #ffffff;
}

.badge.is-demo {
  animation: hue 2s linear infinite;
}

@keyframes hue {
  to {
    filter: hue-rotate(360deg);
  }
}
@media (prefers-reduced-motion: reduce) {
  .badge.is-demo {
    animation: none;
    filter: none;
  }
}

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

export type RainbowBorderBadgeProps = {
  label: string;
  /** 색이 한 바퀴 도는 시간 (기본 2000ms) */
  duration?: number;
};

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

export default function RainbowBorderBadge({ label, duration = 2000 }: RainbowBorderBadgeProps) {
  const vars: Vars = { "--duration": `${duration}ms` };

  return <span className={styles.badge} style={vars}>{label}</span>;
}