* {
    box-sizing: border-box;
}

body {
    margin: 0;
    padding: 0;
    background: radial-gradient(ellipse at center 60%, rgba(150, 180, 210, 0.6) 0%, rgba(45, 75, 110, 0.5) 30%, rgba(5, 12, 25, 0.9) 70%), linear-gradient(to bottom, #02050a 0%, #0a1120 50%, #152033 100%);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    height: 100vh;
    overflow: hidden;
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    color: white;
    position: relative; /* 為了讓 star-bg 定位 */
}

/* === 星空背景特效 === */
.star-bg {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    overflow: hidden;
    pointer-events: none;
    z-index: -1;
}
.star {
    position: absolute;
    background-color: #fff;
    border-radius: 50%;
    animation: twinkle linear infinite;
    box-shadow: 0 0 5px #fff;
}
@keyframes twinkle {
    0% { opacity: 0; transform: scale(0.5); }
    50% { opacity: 1; transform: scale(1.2); }
    100% { opacity: 0; transform: scale(0.5); }
}

.scene {
    width: 100%;
    height: 60vh;
    perspective: 1200px; /* 提供 3D 深度 */
    display: flex;
    align-items: center;
    justify-content: center;
}

.carousel {
    width: 200px;
    height: 200px;
    position: relative;
    transform-style: preserve-3d;
    transform: rotateX(-15deg) rotateY(0deg); /* 傾斜 X 軸讓圓形看起來像橫向橢圓 */
    transition: transform 0.1s linear; /* 平滑旋轉 */
}

.cd-item {
    position: absolute;
    width: 200px;
    height: 200px;
    cursor: pointer;
    transform-style: preserve-3d;
    transition: transform 0.3s, box-shadow 0.3s;
}

.cd-title {
    position: absolute;
    top: -40px;
    left: 0;
    width: 100%;
    text-align: center;
    font-size: 18px;
    font-weight: bold;
    color: #fff;
    text-shadow: 0 2px 4px rgba(0,0,0,0.8);
    transform: translateZ(15px); /* 稍微往前浮現，避免被厚度蓋住 */
    pointer-events: none; /* 避免干擾點擊 */
}

/* 使用 JS 控制各個 cd 的 hover 動效以避免覆蓋 transform 屬性 */

/* === 左上角分類列表 === */
.category-sidebar {
    position: fixed;
    top: 80px; /* 將原本的 20px 往下移，避免被頂部導覽列蓋住 */
    left: 20px;
    background: rgba(0, 0, 0, 0.7); /* 黑色半透明 */
    backdrop-filter: blur(10px); /* 磨砂玻璃特效 (加分質感) */
    padding: 20px;
    border-radius: 16px; /* 圓角 */
    z-index: 100; /* 確保在畫面的上層 */
    min-width: 180px;
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.5); /* 立體陰影 */
}

.category-sidebar h3 {
    margin: 0 0 15px 0;
    font-size: 16px;
    font-weight: 600;
    color: #1ed760; /* Spotify 綠色標題 */
    border-bottom: 1px solid rgba(255, 255, 255, 0.1);
    padding-bottom: 10px;
    letter-spacing: 1px;
}

.category-sidebar ul {
    list-style: none;
    padding: 0;
    margin: 0;
}

.category-sidebar li {
    padding: 10px 15px;
    margin-bottom: 8px;
    cursor: pointer;
    border-radius: 8px; /* 清單項目也做一點小圓角 */
    transition: background 0.3s, color 0.3s;
    font-size: 14px;
    color: #b3b3b3; /* Spotify 次要文字顏色 */
}

.category-sidebar li:hover {
    background: rgba(255, 255, 255, 0.1);
    color: #ffffff;
}

.category-sidebar li.active {
    background: rgba(30, 215, 96, 0.2); /* 淡綠色背景 */
    color: #1ed760;
    font-weight: bold;
}

/* 立體正方形 (3D 厚度) 的各個面 */
.cd-face {
    position: absolute;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
    background-size: cover;
    background-position: center;
    border: 1px solid rgba(255, 255, 255, 0.1);
}

.cd-front {
    transform: translateZ(10px);
    box-shadow: 0 0 15px rgba(0, 0, 0, 0.5);
}

.cd-back {
    background-color: #282828;
    transform: rotateY(180deg) translateZ(10px);
}

.cd-top, .cd-bottom, .cd-left, .cd-right {
    background-color: #000000; /* Spotify 綠色當作厚度顏色 */
}

.cd-top {
    height: 20px;
    transform: rotateX(90deg) translateZ(10px);
    top: -10px;
}

.cd-bottom {
    height: 20px;
    transform: rotateX(-90deg) translateZ(190px);
    top: -10px;
}

.cd-left {
    width: 20px;
    transform: rotateY(-90deg) translateZ(10px);
    left: -10px;
}

.cd-right {
    width: 20px;
    transform: rotateY(90deg) translateZ(190px);
    left: -10px;
}

.controls {
    width: 80%;
    max-width: 600px;
    margin-top: 40px;
    display: flex;
    flex-direction: column;
    align-items: center;
}

input[type=range] {
    -webkit-appearance: none;
    width: 100%;
    height: 8px;
    background: #535353;
    border-radius: 5px;
    outline: none;
    opacity: 0.8;
    transition: opacity .2s;
    cursor: pointer;
}

input[type=range]:hover {
    opacity: 1;
}

input[type=range]::-webkit-slider-thumb {
    -webkit-appearance: none;
    appearance: none;
    width: 20px;
    height: 20px;
    border-radius: 50%;
    background: #1ed760;
    cursor: pointer;
    box-shadow: 0 0 5px rgba(0,0,0,0.5);
}

input[type=range]::-moz-range-thumb {
    width: 20px;
    height: 20px;
    border-radius: 50%;
    background: #1ed760;
    cursor: pointer;
    box-shadow: 0 0 5px rgba(0,0,0,0.5);
    border: none;
}

.instruction {
    margin-top: 15px;
    font-size: 14px;
    color: #b3b3b3;
}

/* === Footer 樣式 === */
footer {
    position: absolute;
    bottom: 0;
    left: 0;
    width: 100%;
    background-color: #000000;
    color: #B7B7B7;
    display: flex;
    flex-direction: column;   
    justify-content: center;
    align-items: center;
    text-align: center;
    font-size: 12px;
    padding: 10px 0;
    z-index: 100;
}

footer p {
    text-align: center;       
    margin: 0;                
    max-width: 90%;           
    word-wrap: break-word;    
}

footer img {
    margin-top: 5px; 
}

/* === Navbar 動畫特效 (來自 announced) === */
.navbar {
  transition: background-color 0.3s ease-in-out;
  backdrop-filter: blur(5px);
}

.nav-link {
  position: relative;
  transition: color 0.3s ease-in-out;
  font-weight: 500;
}

.nav-link::after {
  content: '';
  position: absolute;
  width: 0;
  height: 2px;
  bottom: 0;
  left: 50%;
  background-color: #fff;
  transition: all 0.3s cubic-bezier(0.2, 0.8, 0.2, 1);
}

.nav-link:hover::after {
  width: 100%;
  left: 0;
}

/* Toggler */
.custom-toggler .toggler-icon {
  display: block;
  width: 30px;
  height: 2px;
  margin: 6px 0;
  background-color: #fff;
  transition: all 0.3s cubic-bezier(0.2, 0.8, 0.2, 1);
}

.navbar-toggler {
  padding: 0;
  border: none;
}

.navbar-toggler:focus {
  box-shadow: none;
  outline: none;
}

.custom-toggler[aria-expanded="true"] .toggler-icon:nth-child(1) {
  transform: rotate(-45deg) translate(-5px, 6px);
}

.custom-toggler[aria-expanded="true"] .toggler-icon:nth-child(2) {
  opacity: 0;
}

.custom-toggler[aria-expanded="true"] .toggler-icon:nth-child(3) {
  transform: rotate(45deg) translate(-5px, -6px);
}