04Glow pulse border

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

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

$duration: $dur-loop;                                   // 한 번 번졌다 가라앉는 시간
$easing: $ease-spring;
$color: $subject-blue;                                  // 번짐 색

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

// @property 로 길이를 등록해야 box-shadow 번짐 반경이 중간값을 거치며 부드럽게 바뀐다
@property --glow {
  syntax: "<length>";
  inherits: false;
  initial-value: 0px;
}

.badge {
  display: inline-block;
  border: 2px solid $color;
  border-radius: $r-pill;
  padding: 12px 24px;
  font-weight: 700; font-size: clamp(13px, 3.6vw, 15px); line-height: 1; font-family: inherit;
  color: $stage-ink;
  background: $stage-paper;
  box-shadow: 0 0 var(--glow) 0 rgba($color, .55);
}
.badge.is-demo { animation: glow $duration $easing infinite; }

@keyframes glow {
  0%, 100% { --glow: 0px; }
  50%      { --glow: 16px; }
}

@media (prefers-reduced-motion: reduce) {
  .badge.is-demo { animation: none; --glow: 8px; }
}

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);
}

@property --glow {
  syntax: "<length>";
  inherits: false;
  initial-value: 0px;
}
.badge {
  display: inline-block;
  border: 2px solid #2f6df6;
  border-radius: 999px;
  padding: 12px 24px;
  font-weight: 700;
  font-size: clamp(13px, 3.6vw, 15px);
  line-height: 1;
  font-family: inherit;
  color: #17141a;
  background: #ffffff;
  box-shadow: 0 0 var(--glow) 0 rgba(47, 109, 246, 0.55);
}

.badge.is-demo {
  animation: glow 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

@keyframes glow {
  0%, 100% {
    --glow: 0px;
  }
  50% {
    --glow: 16px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .badge.is-demo {
    animation: none;
    --glow: 8px;
  }
}

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

export type GlowPulseBadgeProps = {
  label: string;
  /** 번졌다 가라앉는 한 번의 시간 (기본 2000ms) */
  duration?: number;
  easing?: string;
  /** 번짐 색 */
  color?: string;
};

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

export default function GlowPulseBadge({
  label,
  duration = 2000,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#2f6df6",
}: GlowPulseBadgeProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

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