03Ô nhập mẫu form đăng ký với nhãn nổi (floating label)

<main class="stage">
  <form class="float-form is-demo" autocomplete="off">
    <div class="float-field float-field--a">
      <input class="float-field__input" id="fname" placeholder=" ">
      <label class="float-field__label" for="fname">Full name</label>
    </div>
    <div class="float-field float-field--b">
      <input class="float-field__input" id="femail" placeholder=" ">
      <label class="float-field__label" for="femail">Email</label>
    </div>
    <button class="float-form__btn" type="button">Create account</button>
  </form>
</main>

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

$duration: $dur-quick;                                 // 라벨이 뜨는 시간
$easing: $ease-out;
$color: $subject-blue;                                 // 포커스 색

@include stage($stage-orange);

.float-form {
  width: min(220px, 82vw);
  display: flex;
  flex-direction: column;
  gap: $sp-5;
}
.float-field {
  position: relative;
}
.float-field__input {
  width: 100%;
  box-sizing: border-box;
  padding: $sp-3 $sp-3 $sp-1;
  border: 1.5px solid #d8d2c4;
  border-radius: $r-sm;
  background: $stage-paper;
  font-size: 13px;
  font-family: inherit;
  color: $stage-ink;
  transition: border-color $duration $easing;
}
.float-field__label {
  position: absolute;
  left: $sp-3;
  top: 50%;
  transform: translateY(-50%);
  font-size: 13px;
  color: #8a8272;
  font-family: inherit;
  pointer-events: none;
  transform-origin: left center; // 규칙8: 입력칸 왼쪽 안쪽선에 맞춰 줄어든다 — 중심이면 줄면서 오른쪽으로 밀린다
  transition: transform $duration $easing, color $duration $easing;
}
.float-field__input:focus { outline: none; border-color: $color; }
.float-field__input:focus + .float-field__label,
.float-field__input:not(:placeholder-shown) + .float-field__label {
  transform: translateY(-135%) scale(.78);
  color: $color;
}
.float-form__btn {
  padding: $sp-2;
  border: none;
  border-radius: $r-sm;
  background: $color;
  color: $stage-paper;
  font-weight: 700;
  font-size: 12px;
  font-family: inherit;
  cursor: pointer;
  transition: transform $dur-instant $ease-out;
}
.float-form__btn:hover, .float-form__btn:focus-visible { transform: translateY(-1px); }

// 자동 재생 미리보기 — 실제 :focus 대신 같은 transform·color 값을 키프레임으로 직접 재생한다
.float-form.is-demo .float-field--a .float-field__input { animation: ring-a $dur-loop $easing infinite; }
.float-form.is-demo .float-field--a .float-field__label { animation: float-a $dur-loop $easing infinite; }
.float-form.is-demo .float-field--b .float-field__input { animation: ring-b $dur-loop $easing infinite; }
.float-form.is-demo .float-field--b .float-field__label { animation: float-b $dur-loop $easing infinite; }

@keyframes float-a {
  0%, 8%   { transform: translateY(-50%) scale(1); color: #8a8272; }
  20%, 45% { transform: translateY(-135%) scale(.78); color: $color; }
  55%, 100% { transform: translateY(-50%) scale(1); color: #8a8272; }
}
@keyframes ring-a {
  0%, 8%    { border-color: #d8d2c4; }
  20%, 45%  { border-color: $color; }
  55%, 100% { border-color: #d8d2c4; }
}
@keyframes float-b {
  0%, 55%   { transform: translateY(-50%) scale(1); color: #8a8272; }
  65%, 92%  { transform: translateY(-135%) scale(.78); color: $color; }
  100%      { transform: translateY(-50%) scale(1); color: #8a8272; }
}
@keyframes ring-b {
  0%, 55%   { border-color: #d8d2c4; }
  65%, 92%  { border-color: $color; }
  100%      { border-color: #d8d2c4; }
}

@media (prefers-reduced-motion: reduce) {
  .float-field__input, .float-field__label, .float-form__btn { transition: none; }
  .float-form.is-demo .float-field--a .float-field__input,
  .float-form.is-demo .float-field--a .float-field__label,
  .float-form.is-demo .float-field--b .float-field__input,
  .float-form.is-demo .float-field--b .float-field__label { animation: none; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.float-form {
  width: min(220px, 82vw);
  display: flex;
  flex-direction: column;
  gap: 20px;
}

.float-field {
  position: relative;
}

.float-field__input {
  width: 100%;
  box-sizing: border-box;
  padding: 12px 12px 4px;
  border: 1.5px solid #d8d2c4;
  border-radius: 8px;
  background: #ffffff;
  font-size: 13px;
  font-family: inherit;
  color: #17141a;
  transition: border-color 220ms ease-out;
}

.float-field__label {
  position: absolute;
  left: 12px;
  top: 50%;
  transform: translateY(-50%);
  font-size: 13px;
  color: #8a8272;
  font-family: inherit;
  pointer-events: none;
  transform-origin: left center;
  transition: transform 220ms ease-out, color 220ms ease-out;
}

.float-field__input:focus {
  outline: none;
  border-color: #2f6df6;
}

.float-field__input:focus + .float-field__label,
.float-field__input:not(:placeholder-shown) + .float-field__label {
  transform: translateY(-135%) scale(0.78);
  color: #2f6df6;
}

.float-form__btn {
  padding: 8px;
  border: none;
  border-radius: 8px;
  background: #2f6df6;
  color: #ffffff;
  font-weight: 700;
  font-size: 12px;
  font-family: inherit;
  cursor: pointer;
  transition: transform 140ms ease-out;
}

.float-form__btn:hover, .float-form__btn:focus-visible {
  transform: translateY(-1px);
}

.float-form.is-demo .float-field--a .float-field__input {
  animation: ring-a 2s ease-out infinite;
}

.float-form.is-demo .float-field--a .float-field__label {
  animation: float-a 2s ease-out infinite;
}

.float-form.is-demo .float-field--b .float-field__input {
  animation: ring-b 2s ease-out infinite;
}

.float-form.is-demo .float-field--b .float-field__label {
  animation: float-b 2s ease-out infinite;
}

@keyframes float-a {
  0%, 8% {
    transform: translateY(-50%) scale(1);
    color: #8a8272;
  }
  20%, 45% {
    transform: translateY(-135%) scale(0.78);
    color: #2f6df6;
  }
  55%, 100% {
    transform: translateY(-50%) scale(1);
    color: #8a8272;
  }
}
@keyframes ring-a {
  0%, 8% {
    border-color: #d8d2c4;
  }
  20%, 45% {
    border-color: #2f6df6;
  }
  55%, 100% {
    border-color: #d8d2c4;
  }
}
@keyframes float-b {
  0%, 55% {
    transform: translateY(-50%) scale(1);
    color: #8a8272;
  }
  65%, 92% {
    transform: translateY(-135%) scale(0.78);
    color: #2f6df6;
  }
  100% {
    transform: translateY(-50%) scale(1);
    color: #8a8272;
  }
}
@keyframes ring-b {
  0%, 55% {
    border-color: #d8d2c4;
  }
  65%, 92% {
    border-color: #2f6df6;
  }
  100% {
    border-color: #d8d2c4;
  }
}
@media (prefers-reduced-motion: reduce) {
  .float-field__input, .float-field__label, .float-form__btn {
    transition: none;
  }
  .float-form.is-demo .float-field--a .float-field__input,
  .float-form.is-demo .float-field--a .float-field__label,
  .float-form.is-demo .float-field--b .float-field__input,
  .float-form.is-demo .float-field--b .float-field__label {
    animation: none;
  }
}

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

export type FloatingLabelInputProps = {
  id: string;
  label: string;
  type?: string;
  /** 라벨이 뜨는 시간 (기본 220ms) */
  duration?: number;
  easing?: string;
  color?: string;
};

/** :placeholder-shown 과 :focus 만으로 동작 — JS 없이 라벨이 뜬다 */
export default function FloatingLabelInput({
  id,
  label,
  type = "text",
  duration = 220,
  easing = "ease-out",
  color = "#2f6df6",
}: FloatingLabelInputProps) {
  const style = { "--duration": `${duration}ms`, "--easing": easing, "--color": color } as CSSProperties;
  return (
    <div className={styles.field} style={style}>
      <input className={styles.input} id={id} type={type} placeholder=" " />
      <label className={styles.label} htmlFor={id}>{label}</label>
    </div>
  );
}