04Viền lỗi nhấp nháy

<main class="stage">
  <div class="bf is-demo">
    <div class="bf__field">
      <input class="bf__input" type="text" placeholder="Số thẻ" value="1234">
      <span class="bf__ring" aria-hidden="true"></span>
    </div>
    <p class="bf__msg">Vui lòng kiểm tra số thẻ</p>
  </div>
</main>

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

$duration: 500ms;                                 // 링이 두 번 깜빡이는 시간
$easing: ease-in-out;
$color: $error;

@include stage($stage-paper);

.bf { width: min(260px, 86vw); display: flex; flex-direction: column; gap: $sp-2; }
.bf__field { position: relative; }
.bf__input {
  box-sizing: border-box;
  width: 100%;
  padding: $sp-2 $sp-3;
  border-radius: $r-sm;
  border: 2px solid rgba(23, 20, 26, .18);
  background: #fff;
  color: $subject-ink;
  font-weight: 400;
  font-size: 14px;
  line-height: 1;
  font-family: inherit;
}
.bf__ring {
  position: absolute;
  inset: -$sp-1;
  border: 2px solid $color;
  border-radius: $r-sm;
  opacity: 0;
  pointer-events: none;
}
.bf__msg { margin: 0; color: $color; font-weight: 500; font-size: 11px; line-height: 1.3; font-family: inherit; }

@keyframes bf-flash {
  0%, 100% { opacity: 0; }
  15% { opacity: 1; }
  30% { opacity: 0; }
  45% { opacity: 1; }
  60% { opacity: 0; }
}
// 실제 동작: 요청이 실패하면 .bf--flash 가 한 번 붙어 두 번 깜빡인다
.bf__ring.bf--flash { animation: bf-flash $duration $easing; }

// 데모 루프
.bf.is-demo .bf__ring { animation: bf-flash $duration $easing infinite; }

@media (prefers-reduced-motion: reduce) {
  .bf__ring.bf--flash,
  .bf.is-demo .bf__ring { animation: none !important; }
}

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);
}

.bf {
  width: min(260px, 86vw);
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.bf__field {
  position: relative;
}

.bf__input {
  box-sizing: border-box;
  width: 100%;
  padding: 8px 12px;
  border-radius: 8px;
  border: 2px solid rgba(23, 20, 26, 0.18);
  background: #fff;
  color: #17141a;
  font-weight: 400;
  font-size: 14px;
  line-height: 1;
  font-family: inherit;
}

.bf__ring {
  position: absolute;
  inset: -4px;
  border: 2px solid #c2361a;
  border-radius: 8px;
  opacity: 0;
  pointer-events: none;
}

.bf__msg {
  margin: 0;
  color: #c2361a;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.3;
  font-family: inherit;
}

@keyframes bf-flash {
  0%, 100% {
    opacity: 0;
  }
  15% {
    opacity: 1;
  }
  30% {
    opacity: 0;
  }
  45% {
    opacity: 1;
  }
  60% {
    opacity: 0;
  }
}
.bf__ring.bf--flash {
  animation: bf-flash 500ms ease-in-out;
}

.bf.is-demo .bf__ring {
  animation: bf-flash 500ms ease-in-out infinite;
}

@media (prefers-reduced-motion: reduce) {
  .bf__ring.bf--flash,
  .bf.is-demo .bf__ring {
    animation: none !important;
  }
}

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

export type ErrorBorderFlashProps = {
  duration?: number;
  easing?: string;
  color?: string;
};

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

export default function ErrorBorderFlash({ duration = 500, easing = "ease-in-out", color = "#c2361a" }: ErrorBorderFlashProps) {
  const [run, setRun] = useState(0);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  return (
    <div className={styles.bf} style={vars}>
      <div className={styles.field}>
        <input className={styles.input} type="text" placeholder="카드 번호" defaultValue="1234" onFocus={() => setRun((n) => n + 1)} />
        <span key={run} className={`${styles.ring} ${styles.flash}`} aria-hidden="true" />
      </div>
      <p className={styles.msg}>카드 번호를 확인하세요</p>
    </div>
  );
}