:root {
    --primary-color: #8B5E34; /* Elegant Brown */
    --secondary-color: #DDA15E; /* Warm Gold Accent */
    --bg-color: #FEFAE0; /* Light Yellow / Cream */
    --card-bg: #FFFFFF;
    --text-main: #4A3B32; /* Dark Brown Text */
    --text-muted: #8C7C73; /* Muted Brown Text */
    --border-color: #E9E1D3; /* Warm soft border */
    --success-color: #606C38; /* Earthy Green for success */
    --danger-color: #BC4749; /* Earthy Red for danger */
    --font-family: 'Inter', sans-serif;
}

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

body {
    font-family: var(--font-family);
    background-color: var(--bg-color);
    color: var(--text-main);
    line-height: 1.6;
}

/* Typography */
h1, h2, h3 { color: var(--primary-color); }
a { color: var(--primary-color); text-decoration: none; }
a:hover { text-decoration: underline; }

/* Utilities */
.hidden { display: none !important; }
.mt-10 { margin-top: 10px; }
.primary-btn {
    background-color: var(--primary-color);
    color: white;
    border: none;
    padding: 10px 20px;
    border-radius: 6px;
    cursor: pointer;
    font-weight: 600;
    width: 100%;
    transition: background 0.3s;
}
.primary-btn:hover { background-color: #004494; }

.success-btn {
    background-color: var(--success-color);
    color: white;
    border: none;
    padding: 8px 16px;
    border-radius: 6px;
    cursor: pointer;
    font-weight: 600;
}
.success-btn:hover { background-color: #27ae60; }

.btn-small { padding: 5px 10px; font-size: 0.85rem; }

/* Auth Screen */
.auth-container {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background: linear-gradient(135deg, #fdfbfb 0%, #ebedee 100%);
}
.auth-box {
    background: var(--card-bg);
    padding: 40px;
    border-radius: 12px;
    box-shadow: 0 10px 25px rgba(0,0,0,0.05);
    width: 100%;
    max-width: 400px;
    text-align: center;
}
.auth-box .logo { width: 120px; margin-bottom: 20px; }
.auth-box h2 { font-size: 1.5rem; margin-bottom: 5px; }
.subtitle { color: var(--text-muted); font-size: 0.9rem; margin-bottom: 25px; }

.input-group {
    text-align: left;
    margin-bottom: 15px;
}
.input-group label {
    display: block;
    font-size: 0.85rem;
    font-weight: 600;
    margin-bottom: 5px;
    color: var(--text-main);
}
.input-group input {
    width: 100%;
    padding: 10px 12px;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    font-size: 1rem;
    font-family: var(--font-family);
}
.input-group input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(139, 94, 52, 0.15); /* Brown shadow */
}
.register-hint { margin-top: 15px; font-size: 0.9rem; }
.alert.warning { background: #fff3cd; color: #856404; padding: 10px; border-radius: 6px; margin-top: 15px; font-size: 0.9rem; }

/* Community Links */
.community-links {
    margin-top: 25px;
    padding-top: 20px;
    border-top: 1px dashed var(--border-color);
}
.community-links p {
    font-size: 0.85rem;
    color: var(--text-muted);
    margin-bottom: 12px;
}
.social-buttons {
    display: flex;
    gap: 10px;
    justify-content: center;
}
.social-btn {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    flex: 1;
    padding: 8px 12px;
    border-radius: 6px;
    font-size: 0.85rem;
    font-weight: 600;
    color: white !important;
    text-decoration: none !important;
    transition: transform 0.2s, box-shadow 0.2s;
}
.social-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 10px rgba(0,0,0,0.1);
}
.zalo-btn { background-color: #0068ff; }
.fb-btn { background-color: #1877f2; }

/* Dashboard Layout */
.dashboard-layout {
    display: flex;
    height: 100vh;
    overflow: hidden;
}

.sidebar {
    width: 250px;
    background: var(--card-bg);
    border-right: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
}
.sidebar-logo { padding: 20px; border-bottom: 1px solid var(--border-color); text-align: center;}
.sidebar-logo img { width: 120px; }
.sidebar-nav { padding: 20px 0; }
.sidebar-nav a {
    display: block;
    padding: 12px 20px;
    color: var(--text-muted);
    font-weight: 500;
    text-decoration: none;
    transition: all 0.2s;
}
.sidebar-nav a.active, .sidebar-nav a:hover {
    background: rgba(139, 94, 52, 0.08); /* Light brown hover */
    color: var(--primary-color);
    border-left: 4px solid var(--primary-color);
}
.sidebar-nav .icon { margin-right: 10px; }

.main-content {
    flex: 1;
    overflow-y: auto;
    display: flex;
    flex-direction: column;
}
.top-header {
    background: var(--card-bg);
    padding: 15px 30px;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    justify-content: space-between;
    align-items: center;
}
.top-header h1 { font-size: 1.2rem; color: var(--text-main); }
.user-profile { display: flex; align-items: center; gap: 10px; }
.avatar {
    width: 35px; height: 35px;
    background: var(--primary-color);
    color: white;
    border-radius: 50%;
    display: flex; justify-content: center; align-items: center;
    font-weight: bold; font-size: 0.9rem;
}

.course-container {
    padding: 30px;
    display: grid;
    grid-template-columns: 2fr 1.2fr;
    gap: 30px;
    max-width: 1400px;
    margin: 0 auto;
    width: 100%;
}

/* Video Section */
.video-section {
    background: var(--card-bg);
    border-radius: 12px;
    padding: 20px;
    box-shadow: 0 4px 15px rgba(0,0,0,0.03);
}
.video-wrapper {
    position: relative;
    padding-bottom: 56.25%; /* 16:9 Aspect Ratio */
    height: 0;
    border-radius: 8px;
    overflow: hidden;
    background: #000;
}
.video-wrapper iframe {
    position: absolute;
    top: 0; left: 0;
    width: 100%; height: 100%;
}
.video-section h2 { margin: 20px 0 15px; font-size: 1.4rem; color: var(--text-main); }
.video-actions { display: flex; gap: 10px; }

/* Playlist Section */
.playlist-section {
    background: var(--card-bg);
    border-radius: 12px;
    padding: 20px;
    box-shadow: 0 4px 15px rgba(0,0,0,0.03);
    display: flex;
    flex-direction: column;
    height: calc(100vh - 140px); /* Fill screen minus header/padding */
}
.playlist-header { margin-bottom: 20px; }
.playlist-header h3 { font-size: 1.1rem; color: var(--text-main); margin-bottom: 10px; }
.progress-bar-container { background: #f9f9f9; padding: 10px 15px; border-radius: 8px; border: 1px solid var(--border-color); }
.progress-info { display: flex; justify-content: space-between; font-size: 0.85rem; font-weight: 600; margin-bottom: 5px;}
.progress-bg { height: 8px; background: #e0e0e0; border-radius: 4px; overflow: hidden; }
.progress-fill { height: 100%; background: var(--success-color); transition: width 0.3s ease; }

.table-container { overflow-y: auto; flex: 1; }
.lesson-table { width: 100%; border-collapse: collapse; }
.lesson-table th, .lesson-table td {
    padding: 12px 10px;
    text-align: left;
    border-bottom: 1px solid var(--border-color);
    font-size: 0.9rem;
}
.lesson-table th { position: sticky; top: 0; background: var(--card-bg); z-index: 1; color: var(--text-muted); font-weight: 600; }
.lesson-table tr { cursor: pointer; transition: background 0.2s; }
.lesson-table tr:hover { background: #f9f9f9; }
.lesson-table tr.playing { background: rgba(139, 94, 52, 0.08); }
.lesson-table tr.playing td:first-child { color: var(--primary-color); font-weight: 600; }

.status-badge {
    padding: 3px 8px; border-radius: 12px; font-size: 0.75rem; font-weight: 600; display: inline-block;
}
.status-badge.completed { background: #e8f8f5; color: var(--success-color); }
.status-badge.pending { background: #fdf2e9; color: var(--secondary-color); }

.task-btn {
    background: white; border: 1px solid var(--secondary-color); color: var(--secondary-color);
    padding: 4px 8px; border-radius: 4px; cursor: pointer; font-size: 0.75rem; font-weight: 600; transition: all 0.2s;
}
.task-btn:hover { background: var(--secondary-color); color: white; }
.task-btn.unlocked { border-color: var(--primary-color); color: var(--primary-color); }
.task-btn.unlocked:hover { background: var(--primary-color); color: white; }

/* Modal */
.modal {
    position: fixed; z-index: 1000; left: 0; top: 0; width: 100%; height: 100%;
    background-color: rgba(0,0,0,0.5); display: flex; justify-content: center; align-items: center;
}
.modal-content {
    background-color: var(--card-bg); padding: 30px; border-radius: 12px; width: 90%; max-width: 400px;
    position: relative; text-align: center; box-shadow: 0 10px 30px rgba(0,0,0,0.2);
}
.close-btn { position: absolute; top: 15px; right: 20px; font-size: 1.5rem; cursor: pointer; color: var(--text-muted); }
.close-btn:hover { color: var(--danger-color); }
.modal-content h3 { margin-bottom: 10px; }
.modal-content p { font-size: 0.9rem; color: var(--text-muted); margin-bottom: 20px; }
.qr-box { background: #f9f9f9; padding: 15px; border-radius: 8px; display: inline-block; margin-bottom: 20px; border: 1px dashed var(--border-color); }
.qr-box img { width: 200px; height: auto; }
.payment-info { text-align: left; background: rgba(139, 94, 52, 0.08); padding: 15px; border-radius: 8px; font-size: 0.85rem; }
.payment-info p { margin-bottom: 5px; color: var(--text-main); }
.highlight { color: var(--danger-color); font-weight: bold; }

/* Responsive */
@media (max-width: 992px) {
    .course-container { grid-template-columns: 1fr; }
    .playlist-section { height: 500px; }
}