01Label nổi (floating label)

<main class="stage">
  <div class="fl is-demo">
    <input id="fl-nick" class="fl__input" type="text" placeholder=" " autocomplete="nickname">
    <span class="fl__bloom" aria-hidden="true"></span>
    <label for="fl-nick" class="fl__label">Biệt danh</label>
  </div>
</main>

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

// ── 변수 4개 ──────────────────────────────────────────
$duration: $dur-quick;                 // 라벨이 떠오르는 시간
$easing: $ease-out;
$spring: cubic-bezier(.3, 1.6, .4, 1); // 스프링 오버슛 — 라벨이 목표 스케일을 살짝 지나쳤다 돌아온다
$color: $subject-cream;                // 포커스 시 라벨·테두리 색

// ── 데모 무대 ──────────────────────────────────────────
@include stage($stage-ink);

.fl {
  position: relative;
  width: min(240px, 82vw);
}

.fl__input {
  box-sizing: border-box;
  width: 100%;
  border: 2px solid rgba($subject-cream, .35);
  border-radius: $r-control;
  padding: $sp-5 $sp-4 $sp-2;
  font-weight: 500;
  font-size: clamp(14px, 4vw, 16px);
  line-height: 1;
  font-family: inherit;
  color: $subject-cream;
  background: transparent;
  position: relative;
  transition: border-color $duration $easing;

  &:focus { outline: none; border-color: $color; }
}

// 테두리 radial 글로우 확산 — 포커스 순간 input 중심에서 바깥으로 번지는 빛 한 겹
.fl__bloom {
  position: absolute;
  inset: -6px;
  border-radius: calc(#{$r-control} + 6px);
  background: radial-gradient(circle, rgba($color, .32) 0%, rgba($color, 0) 70%);
  opacity: 0;
  pointer-events: none;
}
.fl__input:focus ~ .fl__bloom { animation: bloom $dur-base $ease-out; }

.fl__label {
  position: absolute;
  left: $sp-4;
  top: 50%;
  transform: translateY(-50%) scale(1);
  transform-origin: left center; // 규칙8: 인풋 왼쪽 붙은 라벨
  color: rgba($subject-cream, .6);
  font-weight: 500;
  font-size: clamp(14px, 4vw, 16px);
  line-height: 1;
  font-family: inherit;
  pointer-events: none;
  transition: transform $dur-base $spring, color $duration $easing;
}

// 실사용: 포커스거나 값이 있으면(:not(:placeholder-shown)) 라벨이 떠오른다
.fl__input:focus ~ .fl__label,
.fl__input:not(:placeholder-shown) ~ .fl__label {
  transform: translateY(-24px) scale(.78);
  color: $color;
}

// 스프링 오버슛의 실체 — 스케일이 .78 을 지나 .72 까지 줄었다가(.625 초) 제자리로 돌아온다
@keyframes bloom {
  0%   { opacity: 0;   transform: scale(.6); }
  35%  { opacity: 1;   transform: scale(1); }
  100% { opacity: 0;   transform: scale(1.25); }
}

// ── 접근성: 움직임 줄이기 설정이면 즉시 자리만 바뀐다 ──────
@media (prefers-reduced-motion: reduce) {
  .fl__label { transition: none; }
  .fl__input:focus ~ .fl__bloom { animation: none; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.fl {
  position: relative;
  width: min(240px, 82vw);
}

.fl__input {
  box-sizing: border-box;
  width: 100%;
  border: 2px solid rgba(255, 247, 230, 0.35);
  border-radius: 12px;
  padding: 20px 16px 8px;
  font-weight: 500;
  font-size: clamp(14px, 4vw, 16px);
  line-height: 1;
  font-family: inherit;
  color: #fff7e6;
  background: transparent;
  position: relative;
  transition: border-color 220ms ease-out;
}
.fl__input:focus {
  outline: none;
  border-color: #fff7e6;
}

.fl__bloom {
  position: absolute;
  inset: -6px;
  border-radius: calc(12px + 6px);
  background: radial-gradient(circle, rgba(255, 247, 230, 0.32) 0%, rgba(255, 247, 230, 0) 70%);
  opacity: 0;
  pointer-events: none;
}

.fl__input:focus ~ .fl__bloom {
  animation: bloom 300ms ease-out;
}

.fl__label {
  position: absolute;
  left: 16px;
  top: 50%;
  transform: translateY(-50%) scale(1);
  transform-origin: left center;
  color: rgba(255, 247, 230, 0.6);
  font-weight: 500;
  font-size: clamp(14px, 4vw, 16px);
  line-height: 1;
  font-family: inherit;
  pointer-events: none;
  transition: transform 300ms cubic-bezier(0.3, 1.6, 0.4, 1), color 220ms ease-out;
}

.fl__input:focus ~ .fl__label,
.fl__input:not(:placeholder-shown) ~ .fl__label {
  transform: translateY(-24px) scale(0.78);
  color: #fff7e6;
}

@keyframes bloom {
  0% {
    opacity: 0;
    transform: scale(0.6);
  }
  35% {
    opacity: 1;
    transform: scale(1);
  }
  100% {
    opacity: 0;
    transform: scale(1.25);
  }
}
@media (prefers-reduced-motion: reduce) {
  .fl__label {
    transition: none;
  }
  .fl__input:focus ~ .fl__bloom {
    animation: none;
  }
}

// .is-demo 자동 재생: 진짜 focus 를 오가며 :focus 규칙을 그대로 탄다 (3줄)
var el = document.querySelector('.is-demo .fl__input');
var t = function () { document.activeElement === el ? el.blur() : el.focus({ preventScroll: true }); };  // preventScroll — iframe 안 포커스가 홈 그리드의 부모 스크롤을 끌어당기지 않게 (사용자 2026-09-10 실측)
t(); setInterval(t, 400);

import { useState } from "react";
import type { CSSProperties, ChangeEvent } from "react";
import styles from "./FloatingLabel.module.scss";

export type FloatingLabelProps = {
  id?: string;
  label?: string;
  type?: string;
  /** 라벨이 떠오르는 시간(ms) */
  duration?: number;
  easing?: string;
  color?: string;
};

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

export default function FloatingLabel({
  id = "fl-nick",
  label = "Nickname",
  type = "text",
  duration = 220,
  easing = "ease-out",
  color = "#fff7e6",
}: FloatingLabelProps) {
  const [value, setValue] = useState("");
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  return (
    <div className={styles.fl} style={vars}>
      <input
        id={id}
        className={styles.input}
        type={type}
        placeholder=" "
        value={value}
        onChange={(e: ChangeEvent<HTMLInputElement>) => setValue(e.target.value)}
      />
      <span className={styles.bloom} aria-hidden="true" />
      <label htmlFor={id} className={styles.label}>{label}</label>
    </div>
  );
}