:root {
    --bg: #f8fafc;
    --surface: rgba(255, 255, 255, 0.7);
    --border: rgba(0, 0, 0, 0.1);
    --text-primary: #0f172a;
    --text-secondary: #475569;
    --accent: #2563eb;
    --glass-blur: blur(16px);
    --panel-shadow: 0 8px 32px rgba(0, 0, 0, 0.05);
    --instrument-glow: rgba(37, 99, 235, 0.2);
    --transition: all 0.4s cubic-bezier(0.16, 1, 0.3, 1);
}

body.dark-theme {
    --bg: #020617;
    --surface: rgba(15, 23, 42, 0.6);
    --border: rgba(255, 255, 255, 0.08);
    --text-primary: #f1f5f9;
    --text-secondary: #94a3b8;
    --accent: #38bdf8;
    --panel-shadow: 0 12px 48px rgba(0, 0, 0, 0.4);
    --instrument-glow: rgba(56, 189, 248, 0.15);
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
body {
    background-color: var(--bg);
    color: var(--text-primary);
    font-family: 'Inter', sans-serif;
    overflow-x: hidden;
    transition: background-color var(--transition), color var(--transition);
    min-height: 100vh;
    user-select: none; /* UI restriction to prevent text selection */
}

/* --- BACKGROUND ORNAMENTATION --- */
.grid-overlay {
    position: fixed;
    inset: 0;
    background-image: radial-gradient(var(--border) 1px, transparent 1px);
    background-size: 40px 40px;
    z-index: -1;
    opacity: 0.5;
}

.horizon-line {
    position: fixed;
    top: 50%;
    left: 0;
    width: 100%;
    height: 1px;
    background: linear-gradient(90deg, transparent, var(--accent), transparent);
    opacity: 0.1;
    z-index: -1;
}

/* --- HEADER --- */
header {
    padding: 2rem 4rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    backdrop-filter: var(--glass-blur);
    position: sticky;
    top: 0;
    z-index: 100;
}

.logo {
    font-weight: 900;
    font-size: 1.2rem;
    letter-spacing: -0.02em;
    text-transform: uppercase;
    display: flex;
    align-items: center;
    gap: 10px;
}

.logo-symbol {
    width: 24px;
    height: 24px;
    border: 2px solid var(--accent);
    transform: rotate(45deg);
    position: relative;
}

.logo-symbol::after {
    content: '';
    position: absolute;
    inset: 4px;
    background: var(--accent);
}

.controls {
    display: flex;
    gap: 20px;
    align-items: center;
}

.theme-toggle {
    background: var(--surface);
    border: 1px solid var(--border);
    padding: 8px 16px;
    border-radius: 40px;
    color: var(--text-primary);
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.75rem;
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
}

#theme-toggle {
    width: 40px;
    height: 40px;
    padding: 0;
    font-size: 1.1rem;
    border-radius: 50%;
}

.theme-toggle:hover {
    border-color: var(--accent);
    box-shadow: 0 0 15px var(--instrument-glow);
}

/* --- DASHBOARD --- */
main {
    padding: 2rem 4rem;
    max-width: 1600px;
    margin: 0 auto;
}

.hero {
    margin-bottom: 4rem;
}

.hero h1 {
    font-size: 4.5rem;
    font-weight: 900;
    line-height: 1;
    margin-bottom: 1rem;
    letter-spacing: -0.04em;
}

.hero p {
    font-family: 'JetBrains Mono', monospace;
    color: var(--text-secondary);
    font-size: 0.9rem;
    text-transform: uppercase;
}

.course-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 24px;
}

.course-card {
    background: var(--surface);
    border: 1px solid var(--border);
    backdrop-filter: var(--glass-blur);
    padding: 2rem;
    position: relative;
    cursor: pointer;
    transition: var(--transition);
    overflow: hidden;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    min-height: 380px;
}

.course-card:hover {
    transform: translateY(-8px);
    border-color: var(--accent);
    box-shadow: var(--panel-shadow), inset 0 0 20px var(--instrument-glow);
}

.course-card::before {
    content: '';
    position: absolute;
    top: 0;
    right: 0;
    width: 60px;
    height: 60px;
    background: linear-gradient(225deg, var(--accent), transparent 70%);
    opacity: 0;
    transition: var(--transition);
}

.course-card:hover::before {
    opacity: 0.2;
}

.course-id {
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.7rem;
    color: var(--accent);
    margin-bottom: 1rem;
    display: block;
}

.course-title {
    font-size: 1.75rem;
    font-weight: 700;
    margin-bottom: 1rem;
    line-height: 1.1;
}

.course-meta {
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.75rem;
    color: var(--text-secondary);
    margin-top: auto;
}

/* Instrumental Decoration */
.card-gauge {
    width: 100%;
    height: 2px;
    background: var(--border);
    margin: 20px 0;
    position: relative;
    overflow: hidden;
}

.gauge-fill {
    position: absolute;
    left: 0;
    top: 0;
    height: 100%;
    width: 0%;
    background: var(--accent);
    transition: width 0.6s cubic-bezier(0.16, 1, 0.3, 1);
    box-shadow: 0 0 10px var(--instrument-glow);
}

/* --- PLAYER VIEW (Overlay) --- */
#player-overlay {
    position: fixed;
    inset: 0;
    background: var(--bg);
    z-index: 1000;
    display: none;
    padding: 2rem;
    grid-template-columns: 1fr 350px;
    gap: 2rem;
    animation: slideUp 0.6s cubic-bezier(0.16, 1, 0.3, 1);
}

@keyframes slideUp {
    from {
        transform: translateY(100%);
        opacity: 0;
    }

    to {
        transform: translateY(0);
        opacity: 1;
    }
}

.video-container {
    background: #000;
    border-radius: 4px;
    position: relative;
    overflow: hidden;
    display: flex;
    align-items: center;
    justify-content: center;
    border: 1px solid var(--border);
    aspect-ratio: 16 / 9;
}

.video-container iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}

.video-placeholder {
    color: white;
    text-align: center;
}

.player-sidebar {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.sidebar-panel {
    background: var(--surface);
    border: 1px solid var(--border);
    backdrop-filter: var(--glass-blur);
    padding: 1.5rem;
    flex: 1;
}

.close-player {
    position: absolute;
    top: 2rem;
    right: 2rem;
    background: var(--accent);
    color: white;
    border: none;
    padding: 10px 20px;
    font-family: 'JetBrains Mono', monospace;
    font-weight: bold;
    cursor: pointer;
    z-index: 1001;
}

.instrument-data {
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.8rem;
    color: var(--accent);
    margin-bottom: 0.5rem;
}

.tag {
    display: inline-block;
    padding: 4px 12px;
    border: 1px solid var(--accent);
    font-size: 0.65rem;
    text-transform: uppercase;
    margin-right: 8px;
    font-weight: bold;
}

/* Locked Cards */
.course-card.locked {
    opacity: 0.6;
    cursor: not-allowed;
    pointer-events: none;
    filter: grayscale(0.5);
    background: rgba(15, 23, 42, 0.2);
}

.lock-icon {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 48px;
    height: 48px;
    color: var(--text-secondary);
    opacity: 0.3;
    z-index: 5;
}

.course-card.locked .course-title,
.course-card.locked .tag,
.course-card.locked .course-id {
    opacity: 0.4;
}

/* Responsive */
@media (max-width: 1024px) {
    #player-overlay {
        grid-template-columns: 1fr;
        overflow-y: auto;
    }

    .hero h1 {
        font-size: 3rem;
    }
}

/* --- CHECKBOX STYLING --- */
.sidebar-panel ul li {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 8px;
}

.sidebar-panel input[type="checkbox"] {
    appearance: none;
    -webkit-appearance: none;
    width: 18px;
    height: 18px;
    border: 2px solid var(--accent);
    border-radius: 2px;
    background: transparent;
    cursor: pointer;
    position: relative;
    transition: var(--transition);
}

.sidebar-panel input[type="checkbox"]:checked {
    background: var(--accent);
}

.sidebar-panel input[type="checkbox"]:checked::after {
    content: '✓';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    color: white;
    font-size: 12px;
    font-weight: bold;
}

.sidebar-panel input[type="checkbox"]:hover {
    box-shadow: 0 0 10px var(--instrument-glow);
}

/* Video List Improvements */
.video-list-container {
    max-height: 400px;
    overflow-y: auto;
    padding-right: 10px;
}

.video-list-container::-webkit-scrollbar {
    width: 4px;
}

.video-list-container::-webkit-scrollbar-thumb {
    background: var(--accent);
    border-radius: 10px;
}

#video-list li {
    padding: 8px;
    border-radius: 4px;
    cursor: pointer;
    transition: var(--transition);
    border-bottom: 1px solid var(--border);
}

#video-list li:hover {
    background: var(--instrument-glow);
}

#video-list li input[type="checkbox"] {
    margin-right: 8px;
    cursor: pointer;
}