:root {
    --primary: #7B6CF6;
    --primary-dark: #2D1B8E;
    --primary-light: #EAE8FD;
    --bg-dark: #0F092A;
    --bg-light: #F4F3FF;
    --text-main: #333333;
    --text-muted: #666666;
    --white: #FFFFFF;
    --border: #E5E5E5;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: 'Inter', 'Noto Sans SC', sans-serif;
    background-color: var(--bg-dark);
    color: var(--text-main);
    height: 100vh;
    overflow: hidden;
}

.app-container {
    display: flex;
    height: 100vh;
    width: 100vw;
}

/* Sidebar General */
.sidebar {
    height: 100%;
    overflow-y: auto;
    background: var(--white);
    border-right: 1px solid var(--border);
    display: block; /* 移除 flex，避免高度干扰 */
}

/* Column 1: Courses */
.column-courses {
    width: 240px;
    flex-shrink: 0;
    background-color: var(--bg-dark);
    color: var(--white);
    border-right: 1px solid rgba(255,255,255,0.1);
}

.brand {
    padding: 30px 24px;
    display: flex;
    align-items: center;
    gap: 12px;
}

.logo {
    color: var(--primary);
    font-size: 24px;
}

.brand h1 {
    font-size: 20px;
    font-weight: 800;
    letter-spacing: 1px;
}

.badge {
    background: var(--primary);
    font-size: 10px;
    padding: 2px 6px;
    border-radius: 4px;
    font-weight: 600;
    white-space: nowrap;
}

.menu-list {
    list-style: none;
    padding: 0 16px;
}

.menu-list li {
    padding: 14px 16px;
    margin-bottom: 8px;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s ease;
    font-size: 14px;
    font-weight: 500;
}

.column-courses .menu-list li {
    color: rgba(255,255,255,0.7);
}

.column-courses .menu-list li:hover {
    background: rgba(123, 108, 246, 0.1);
    color: var(--white);
}

.column-courses .menu-list li.active {
    background: var(--primary);
    color: var(--white);
    box-shadow: 0 4px 12px rgba(123, 108, 246, 0.3);
}

/* Column 2: Lessons */
.column-lessons {
    width: 320px; 
    flex-shrink: 0;
    background: #F8F9FA;
}

.column-header {
    padding: 30px 24px 20px;
    position: sticky;
    top: 0;
    background: #F8F9FA;
    z-index: 5;
    border-bottom: 1px solid var(--border);
}

.column-header h2 {
    font-size: 16px;
    font-weight: 700;
    color: var(--primary-dark);
}

.column-lessons .menu-list {
    padding: 16px;
}

.column-lessons .menu-list li {
    background: var(--white);
    border: 1px solid var(--border);
    color: var(--text-main);
    box-shadow: 0 2px 4px rgba(0,0,0,0.02);
    padding: 16px;
    display: block; /* 移除 flex 避免挤压 */
    margin-bottom: 12px;
}

.column-lessons .menu-list li div:first-child {
    font-size: 14px;
    line-height: 1.5;
    font-weight: 600;
    margin-bottom: 6px;
}

.column-lessons .menu-list li:hover {
    border-color: var(--primary-light);
    transform: translateY(-1px);
    box-shadow: 0 4px 8px rgba(0,0,0,0.05);
}

.column-lessons .menu-list li.active {
    border-color: var(--primary);
    background: var(--primary-light);
    color: var(--primary-dark);
}

.lesson-meta {
    font-size: 12px !important;
    color: var(--text-muted);
    font-weight: 400 !important;
}

/* Column 3: Content */
.column-content {
    flex-grow: 1;
    background: #EDECF5;
    position: relative;
    height: 100%;
}

.placeholder {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    text-align: center;
    color: var(--text-muted);
}

.placeholder .icon {
    font-size: 48px;
    margin-bottom: 16px;
    opacity: 0.5;
}

.viewer {
    display: flex;
    flex-direction: column;
    height: 100%;
    width: 100%;
}

.viewer.hidden {
    display: none;
}

.viewer-header {
    padding: 24px 30px;
    background: var(--white);
    border-bottom: 1px solid var(--border);
    box-shadow: 0 2px 10px rgba(0,0,0,0.02);
    z-index: 10;
    flex-shrink: 0;
}

.viewer-header h2 {
    font-size: 20px;
    font-weight: 700;
    color: var(--primary-dark);
}

.slides-list {
    flex-grow: 1;
    overflow-y: auto;
    padding: 40px;
}

.slide-card {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto 60px auto; /* 居中并设置下边距 */
    background: var(--white);
    border-radius: 12px;
    overflow: hidden;
    box-shadow: 0 10px 30px rgba(45, 27, 142, 0.1);
    /* 核心修复：移除 flex-direction column，改成普通的块级显示 */
    display: block; 
}

.slide-image-wrapper {
    width: 100%;
    position: relative;
    background: #000;
    /* 核心修复：设置一个最小比例，让图片可以顺利撑开高度 */
    aspect-ratio: 16 / 9;
}

.slide-image-wrapper img {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    object-fit: cover; /* 保证充满16:9盒子且不压缩 */
    display: block;
}

.slide-badge {
    position: absolute;
    bottom: 16px;
    right: 16px;
    background: rgba(0,0,0,0.6);
    color: white;
    padding: 6px 12px;
    border-radius: 20px;
    font-size: 14px;
    font-weight: 600;
    backdrop-filter: blur(4px);
    z-index: 2;
}

.slide-script {
    padding: 30px 40px;
    background: #FFFFFF;
    border-top: 1px solid var(--border);
}

.slide-script-header {
    font-size: 15px;
    font-weight: 700;
    color: var(--primary-dark);
    margin-bottom: 16px;
    display: flex;
    align-items: center;
    gap: 8px;
}

.slide-script-text {
    font-size: 16px;
    line-height: 2;
    color: #333333;
    white-space: pre-wrap;
}

/* Custom Scrollbar */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}
::-webkit-scrollbar-track {
    background: rgba(0,0,0,0.02);
}
::-webkit-scrollbar-thumb {
    background: rgba(0,0,0,0.15);
    border-radius: 4px;
}
::-webkit-scrollbar-thumb:hover {
    background: rgba(0,0,0,0.3);
}