07Sticky apply-bar reveal — a bottom bar repositioned by a selection-state value

<main class="stage" id="stage">
  <div class="options">
    <label class="option"><input class="option__input" type="checkbox" data-idx="0"> Free shipping</label>
    <label class="option"><input class="option__input" type="checkbox" data-idx="1"> Same-day dispatch</label>
  </div>
  <div class="apply-bar is-demo" id="bar">
    <span class="apply-bar__label">2 selected</span>
    <button class="apply-bar__btn" type="button">Apply</button>
  </div>
</main>

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

$duration: $dur-enter;
$easing: $ease-spring;
$color: $subject-cream;

@include stage($stage-orange);

.stage {
  position: relative;
  overflow: hidden;
}

.options {
  display: flex;
  flex-direction: column;
  gap: $sp-3;
}

.option {
  display: flex;
  align-items: center;
  gap: $sp-2;
  color: $subject-ink;
  font-weight: 500;
  font-size: 13px;
  line-height: 1.4;
}

.option__input {
  width: 16px;
  height: 16px;
  accent-color: $subject-ink;
}

.apply-bar {
  box-sizing: border-box;
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: $sp-3 $sp-4;
  background: $color;
  color: $subject-ink;
  box-shadow: $shadow-raised;
  transform: translateY(100%);
  transition: transform $duration $easing;
}

.apply-bar__label {
  font-weight: 600;
  font-size: 12px;
  line-height: 1.3;
}

.apply-bar__btn {
  border: 0;
  border-radius: $r-pill;
  padding: $sp-2 $sp-4;
  background: $subject-ink;
  color: $color;
  font-family: inherit;
  font-weight: 600;
  font-size: 12px;
  line-height: 1.3;
  cursor: pointer;
}

.stage.has-selection .apply-bar {
  transform: translateY(0);
}

.apply-bar.is-demo {
  animation-name: bar-loop;
  animation-duration: $dur-loop;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}

@keyframes bar-loop {
  0%, 15% { transform: translateY(100%); }
  40%, 75% { transform: translateY(0); }
  100% { transform: translateY(100%); }
}

@media (max-width: 340px) {
  .apply-bar { padding: $sp-2 $sp-3; }
  .options { gap: $sp-2; }
}

@media (prefers-reduced-motion: reduce) {
  .apply-bar { transition: none; }
  .apply-bar.is-demo { animation: none; transform: translateY(0); opacity: .96; }
}

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);
}

.stage {
  position: relative;
  overflow: hidden;
}

.options {
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.option {
  display: flex;
  align-items: center;
  gap: 8px;
  color: #17141a;
  font-weight: 500;
  font-size: 13px;
  line-height: 1.4;
}

.option__input {
  width: 16px;
  height: 16px;
  accent-color: #17141a;
}

.apply-bar {
  box-sizing: border-box;
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 16px;
  background: #fff7e6;
  color: #17141a;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  transform: translateY(100%);
  transition: transform 600ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.apply-bar__label {
  font-weight: 600;
  font-size: 12px;
  line-height: 1.3;
}

.apply-bar__btn {
  border: 0;
  border-radius: 999px;
  padding: 8px 16px;
  background: #17141a;
  color: #fff7e6;
  font-family: inherit;
  font-weight: 600;
  font-size: 12px;
  line-height: 1.3;
  cursor: pointer;
}

.stage.has-selection .apply-bar {
  transform: translateY(0);
}

.apply-bar.is-demo {
  animation-name: bar-loop;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
}

@keyframes bar-loop {
  0%, 15% {
    transform: translateY(100%);
  }
  40%, 75% {
    transform: translateY(0);
  }
  100% {
    transform: translateY(100%);
  }
}
@media (max-width: 340px) {
  .apply-bar {
    padding: 8px 12px;
  }
  .options {
    gap: 8px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .apply-bar {
    transition: none;
  }
  .apply-bar.is-demo {
    animation: none;
    transform: translateY(0);
    opacity: 0.96;
  }
}

// 필터가 하나라도 선택되어 있는지(불 값)만 보고 바 위치를 translateY 로 보간한다.
// 실제 체크박스 변경: classList.toggle 로 has-selection 상태를 뒤집는다.
(function () {
  var stage = document.getElementById('stage');
  var bar = document.getElementById('bar');
  var inputs = document.querySelectorAll('.option__input');
  if (!stage || !bar || !inputs.length) return;

  function sync() {
    bar.classList.remove('is-demo');
    var any = Array.prototype.some.call(inputs, function (input) {
      return input.checked;
    });
    stage.classList.toggle('has-selection', any);
  }

  inputs.forEach(function (input) {
    input.addEventListener('change', sync);
  });
})();

import { useEffect, useRef } from "react";
import styles from "./StickyApplyBarReveal.module.scss";

// 필터가 하나라도 선택되어 있는지(불 값)만 보고 바 위치를 translateY 로 보간한다.
// 실제 체크박스 변경: classList.toggle 로 has-selection 상태를 뒤집는다.
export default function StickyApplyBarReveal() {
  const stageRef = useRef<HTMLElement>(null);
  const barRef = useRef<HTMLDivElement>(null);
  const input0Ref = useRef<HTMLInputElement>(null);
  const input1Ref = useRef<HTMLInputElement>(null);

  useEffect(() => {
    const stage = stageRef.current;
    const bar = barRef.current;
    const inputs = [input0Ref.current, input1Ref.current].filter(
      (x): x is HTMLInputElement => x !== null
    );
    if (!stage || !bar || inputs.length === 0) return;

    function sync() {
      bar!.classList.remove(styles["is-demo"]);
      const anySelected = inputs.some((input) => input.checked);
      stage!.classList.toggle(styles["has-selection"], anySelected);
    }

    inputs.forEach((input) => input.addEventListener("change", sync));
    return () => {
      inputs.forEach((input) => input.removeEventListener("change", sync));
    };
  }, []);

  return (
    <main ref={stageRef} className={styles.stage}>
      <div className={styles.options}>
        <label className={styles.option}>
          <input ref={input0Ref} className={styles.option__input} type="checkbox" /> 무료 배송
        </label>
        <label className={styles.option}>
          <input ref={input1Ref} className={styles.option__input} type="checkbox" /> 당일 출고
        </label>
      </div>
      <div ref={barRef} className={`${styles["apply-bar"]} ${styles["is-demo"]}`}>
        <span className={styles["apply-bar__label"]}>2개 선택됨</span>
        <button className={styles["apply-bar__btn"]} type="button">
          적용하기
        </button>
      </div>
    </main>
  );
}