06Mega-menu background fill

<main class="stage">
  <nav class="menu is-demo">
    <button class="menu__trigger" type="button" aria-expanded="false">Categories</button>
    <div class="menu__panel">
      <div class="menu__fill"></div>
      <div class="menu__grid">
        <a href="#">Women</a>
        <a href="#">Men</a>
        <a href="#">Kids</a>
        <a href="#">Home</a>
      </div>
    </div>
  </nav>
</main>

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

$duration: $dur-base;                              // 배경이 번지는 시간
$easing: $ease-out;                                // 시작 빠르고 끝은 부드럽게
$color: $stage-ink;                                // 트리거 버튼 색 (노란 무대와 대비)

@include stage($stage-yellow);

.menu {
  position: relative;
  align-self: flex-start;                            // 패널이 트리거 아래로 열려 무대 중앙에 두면 320px 에서 아래로 넘친다 — 위로 붙여 여유를 둔다 (실측 320px 재검증 2026-09-10)
  justify-self: start;                                // 패널이 260px 까지 오른쪽으로 늘어나는데 트리거가 무대 가운데라 320px 에서 오른쪽으로도 넘친다 — 왼쪽에 붙인다
  font-weight: 500;
  font-size: clamp(13px, 3.6vw, 16px);
  line-height: 1.4;
  font-family: inherit;

  &__trigger {
    border: 0;
    border-radius: $r-control;
    padding: clamp(9px, 3vw, 13px) clamp(16px, 4vw, 22px);
    font-weight: 700;
    font-family: inherit;
    color: $subject-cream;
    background: $color;
    cursor: pointer;
  }

  &__panel {
    position: absolute;
    top: calc(100% + 8px);
    left: 0;
    width: min(260px, 90vw);
    padding: 4px;
    pointer-events: none;
  }

  // 배경이 왼쪽부터 옆으로 번지듯 채워진다 (transform 만 움직인다)
  &__fill {
    position: absolute;
    inset: 0;
    background: $subject-cream;
    border-radius: $r-card;
    box-shadow: $shadow-raised;
    transform: scaleX(0);
    transform-origin: left; // 규칙8: 왼쪽부터 번짐
  }

  &__grid {
    position: relative;
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 4px;
    padding: 8px;
    opacity: 0;
  }
  &__grid a {
    padding: 8px 10px;
    border-radius: $r-control - 4px;
    color: $stage-ink;
    text-decoration: none;
    text-align: center;
  }
  &__grid a:hover { background: rgba($stage-ink, .06); }

  &.is-open &__fill  { transform: scaleX(1); pointer-events: auto; transition: transform $duration $easing; }
  &.is-open &__grid  { opacity: 1; pointer-events: auto; transition: opacity $duration $easing $duration * .4; }
  &.is-demo &__fill  { animation: fill-loop $dur-loop $easing infinite; }
  &.is-demo &__grid  { animation: grid-loop $dur-loop $easing infinite; }
}

@keyframes fill-loop {
  0%, 25%   { transform: scaleX(0); }
  45%, 80%  { transform: scaleX(1); }
  95%, 100% { transform: scaleX(0); }
}
@keyframes grid-loop {
  0%, 33%   { opacity: 0; }
  50%, 78%  { opacity: 1; }
  92%, 100% { opacity: 0; }
}

@media (prefers-reduced-motion: reduce) {
  .menu__fill, .menu__grid { transition: none !important; }
  .menu.is-demo .menu__fill, .menu.is-demo .menu__grid { animation: none; }
  .menu.is-demo .menu__fill { transform: scaleX(0); }
  .menu.is-demo .menu__grid { opacity: 0; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.menu {
  position: relative;
  align-self: flex-start;
  justify-self: start;
  font-weight: 500;
  font-size: clamp(13px, 3.6vw, 16px);
  line-height: 1.4;
  font-family: inherit;
}
.menu__trigger {
  border: 0;
  border-radius: 12px;
  padding: clamp(9px, 3vw, 13px) clamp(16px, 4vw, 22px);
  font-weight: 700;
  font-family: inherit;
  color: #fff7e6;
  background: #17141a;
  cursor: pointer;
}
.menu__panel {
  position: absolute;
  top: calc(100% + 8px);
  left: 0;
  width: min(260px, 90vw);
  padding: 4px;
  pointer-events: none;
}
.menu__fill {
  position: absolute;
  inset: 0;
  background: #fff7e6;
  border-radius: 16px;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  transform: scaleX(0);
  transform-origin: left;
}
.menu__grid {
  position: relative;
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 4px;
  padding: 8px;
  opacity: 0;
}
.menu__grid a {
  padding: 8px 10px;
  border-radius: 8px;
  color: #17141a;
  text-decoration: none;
  text-align: center;
}
.menu__grid a:hover {
  background: rgba(23, 20, 26, 0.06);
}
.menu.is-open .menu__fill {
  transform: scaleX(1);
  pointer-events: auto;
  transition: transform 300ms ease-out;
}
.menu.is-open .menu__grid {
  opacity: 1;
  pointer-events: auto;
  transition: opacity 300ms ease-out 120ms;
}
.menu.is-demo .menu__fill {
  animation: fill-loop 2s ease-out infinite;
}
.menu.is-demo .menu__grid {
  animation: grid-loop 2s ease-out infinite;
}

@keyframes fill-loop {
  0%, 25% {
    transform: scaleX(0);
  }
  45%, 80% {
    transform: scaleX(1);
  }
  95%, 100% {
    transform: scaleX(0);
  }
}
@keyframes grid-loop {
  0%, 33% {
    opacity: 0;
  }
  50%, 78% {
    opacity: 1;
  }
  92%, 100% {
    opacity: 0;
  }
}
@media (prefers-reduced-motion: reduce) {
  .menu__fill, .menu__grid {
    transition: none !important;
  }
  .menu.is-demo .menu__fill, .menu.is-demo .menu__grid {
    animation: none;
  }
  .menu.is-demo .menu__fill {
    transform: scaleX(0);
  }
  .menu.is-demo .menu__grid {
    opacity: 0;
  }
}

// 트리거를 클릭하면 열리고 닫힌다. 데모(.is-demo)는 스스로 반복한다.
var m = document.querySelector('.menu'), t = m.querySelector('.menu__trigger');
t.addEventListener('click', function () {
  m.classList.remove('is-demo');
  t.setAttribute('aria-expanded', m.classList.toggle('is-open'));
});

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

export type MegaMenuFillDropdownProps = {
  triggerLabel: string;
  categories: string[];
  /** 배경이 번지는 시간 (기본 300ms) */
  duration?: number;
  easing?: string;
  color?: string;
};

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

export default function MegaMenuFillDropdown({
  triggerLabel,
  categories,
  duration = 300,
  easing = "ease-out",
  color = "#17141a",
}: MegaMenuFillDropdownProps) {
  const [open, setOpen] = useState(false);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  return (
    <nav className={styles.menu} style={vars}>
      <button type="button" className={styles.trigger} aria-expanded={open} onClick={() => setOpen((v) => !v)}>
        {triggerLabel}
      </button>
      <div className={open ? `${styles.panel} ${styles.panelOpen}` : styles.panel}>
        <div className={styles.fill} />
        <div className={styles.grid}>
          {categories.map((label) => (
            <a key={label} href="#">{label}</a>
          ))}
        </div>
      </div>
    </nav>
  );
}