/* CSS Variables for theming */
:root {
    --primary-color: #6366f1;
    --primary-hover: #4f46e5;
    --secondary-color: #10b981;
    --accent-color: #f59e0b;
    --danger-color: #ef4444;
    --background: #0f172a;
    --surface: #1e293b;
    --surface-light: #334155;
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    --border-color: #475569;
    --success-bg: #065f46;
    --error-bg: #7f1d1d;
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.4);
}

/* Reset and base styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
    background: var(--background);
    color: var(--text-primary);
    min-height: 100vh;
    line-height: 1.6;
}

.app-container {
    max-width: 800px;
    margin: 0 auto;
    padding: 20px;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* Header */
header {
    text-align: center;
    padding: 30px 0;
}

header h1 {
    font-size: 2.5rem;
    margin-bottom: 10px;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.tagline {
    color: var(--text-secondary);
    font-size: 1.1rem;
}

/* Main content */
main {
    flex: 1;
}

/* Mode Selection */
.mode-selection {
    display: flex;
    gap: 10px;
    justify-content: center;
    margin-bottom: 25px;
}

.mode-btn {
    padding: 12px 24px;
    border: 2px solid var(--border-color);
    background: var(--surface);
    color: var(--text-primary);
    border-radius: 8px;
    cursor: pointer;
    font-size: 1rem;
    transition: all 0.3s ease;
}

.mode-btn:hover {
    border-color: var(--primary-color);
    background: var(--surface-light);
}

.mode-btn.active {
    border-color: var(--primary-color);
    background: var(--primary-color);
}

/* Settings Panel */
.settings-panel {
    display: flex;
    flex-wrap: wrap;
    gap: 15px;
    justify-content: center;
    padding: 20px;
    background: var(--surface);
    border-radius: 12px;
    margin-bottom: 25px;
}

.setting-group {
    display: flex;
    flex-direction: column;
    gap: 5px;
}

.setting-group label {
    font-size: 0.85rem;
    color: var(--text-secondary);
}

.setting-group select {
    padding: 10px 15px;
    border: 1px solid var(--border-color);
    background: var(--surface-light);
    color: var(--text-primary);
    border-radius: 6px;
    font-size: 0.95rem;
    cursor: pointer;
    min-width: 160px;
}

.setting-group select:focus {
    outline: none;
    border-color: var(--primary-color);
}

/* Score Display */
.score-display {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 15px;
    margin-bottom: 25px;
}

.score-item {
    background: var(--surface);
    padding: 15px;
    border-radius: 10px;
    text-align: center;
    box-shadow: var(--shadow);
}

.score-label {
    display: block;
    font-size: 0.8rem;
    color: var(--text-secondary);
    margin-bottom: 5px;
}

.score-value {
    display: block;
    font-size: 1.5rem;
    font-weight: bold;
    color: var(--primary-color);
}

/* Play Controls */
.play-controls {
    display: flex;
    gap: 15px;
    justify-content: center;
    margin-bottom: 30px;
}

.play-btn, .replay-btn {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 15px 30px;
    border: none;
    border-radius: 12px;
    font-size: 1.1rem;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: var(--shadow);
}

.play-btn {
    background: linear-gradient(135deg, var(--primary-color), var(--primary-hover));
    color: white;
}

.play-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.replay-btn {
    background: var(--surface-light);
    color: var(--text-primary);
}

.replay-btn:hover:not(:disabled) {
    background: var(--surface);
}

.replay-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

.play-icon, .replay-icon {
    font-size: 1.2rem;
}

/* Interval Training */
.interval-training, .melody-training {
    background: var(--surface);
    padding: 25px;
    border-radius: 12px;
    margin-bottom: 25px;
}

.interval-training h2, .melody-training h2 {
    text-align: center;
    margin-bottom: 10px;
    font-size: 1.4rem;
}

.instruction {
    text-align: center;
    color: var(--text-secondary);
    margin-bottom: 20px;
}

.interval-buttons {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: 10px;
}

.interval-btn {
    padding: 15px 10px;
    border: 2px solid var(--border-color);
    background: var(--surface-light);
    color: var(--text-primary);
    border-radius: 8px;
    cursor: pointer;
    font-size: 0.95rem;
    transition: all 0.2s ease;
}

.interval-btn:hover {
    border-color: var(--primary-color);
    background: rgba(99, 102, 241, 0.2);
}

.interval-btn.correct {
    border-color: var(--secondary-color);
    background: var(--success-bg);
}

.interval-btn.incorrect {
    border-color: var(--danger-color);
    background: var(--error-bg);
}

.interval-btn:disabled {
    cursor: not-allowed;
}

/* Piano Keyboard */
.piano-keyboard {
    display: flex;
    justify-content: center;
    margin: 20px 0;
    position: relative;
    height: 150px;
}

.piano-key {
    position: relative;
    cursor: pointer;
    transition: all 0.1s ease;
}

.piano-key.white {
    width: 45px;
    height: 150px;
    background: linear-gradient(180deg, #fff 0%, #e8e8e8 100%);
    border: 1px solid #999;
    border-radius: 0 0 5px 5px;
    z-index: 1;
    margin: 0 1px;
}

.piano-key.white:hover {
    background: linear-gradient(180deg, #f0f0f0 0%, #d8d8d8 100%);
}

.piano-key.white:active, .piano-key.white.active {
    background: linear-gradient(180deg, #ddd 0%, #ccc 100%);
}

.piano-key.black {
    width: 30px;
    height: 90px;
    background: linear-gradient(180deg, #333 0%, #000 100%);
    border-radius: 0 0 4px 4px;
    position: absolute;
    z-index: 2;
}

.piano-key.black:hover {
    background: linear-gradient(180deg, #444 0%, #111 100%);
}

.piano-key.black:active, .piano-key.black.active {
    background: linear-gradient(180deg, #555 0%, #222 100%);
}

.piano-key.selected {
    box-shadow: 0 0 10px var(--primary-color);
}

.key-label {
    position: absolute;
    bottom: 10px;
    left: 50%;
    transform: translateX(-50%);
    font-size: 0.75rem;
    color: #666;
    pointer-events: none;
}

.piano-key.black .key-label {
    color: #aaa;
}

/* Melody Progress */
.melody-display {
    text-align: center;
    margin-bottom: 15px;
}

.melody-progress {
    display: flex;
    justify-content: center;
    gap: 10px;
    flex-wrap: wrap;
}

.progress-dot {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    background: var(--surface-light);
    border: 2px solid var(--border-color);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.8rem;
    font-weight: bold;
}

.progress-dot.filled {
    border-color: var(--primary-color);
    background: var(--primary-color);
}

.progress-dot.correct {
    border-color: var(--secondary-color);
    background: var(--secondary-color);
}

.progress-dot.incorrect {
    border-color: var(--danger-color);
    background: var(--danger-color);
}

/* Melody Controls */
.melody-controls {
    display: flex;
    gap: 15px;
    justify-content: center;
    margin-top: 20px;
}

.clear-btn, .submit-btn {
    padding: 12px 30px;
    border: none;
    border-radius: 8px;
    font-size: 1rem;
    cursor: pointer;
    transition: all 0.2s ease;
}

.clear-btn {
    background: var(--surface-light);
    color: var(--text-primary);
}

.clear-btn:hover {
    background: var(--border-color);
}

.submit-btn {
    background: var(--secondary-color);
    color: white;
}

.submit-btn:hover:not(:disabled) {
    background: #059669;
}

.submit-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* Feedback */
.feedback {
    margin-bottom: 25px;
    min-height: 60px;
}

.feedback-content {
    padding: 15px 20px;
    border-radius: 10px;
    text-align: center;
    font-size: 1.1rem;
    font-weight: 500;
    animation: fadeIn 0.3s ease;
}

.feedback-content.success {
    background: var(--success-bg);
    border: 1px solid var(--secondary-color);
}

.feedback-content.error {
    background: var(--error-bg);
    border: 1px solid var(--danger-color);
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(-10px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Statistics */
.statistics {
    background: var(--surface);
    padding: 25px;
    border-radius: 12px;
    margin-bottom: 25px;
}

.statistics h3 {
    text-align: center;
    margin-bottom: 20px;
    color: var(--text-secondary);
}

.stats-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 15px;
    margin-bottom: 20px;
}

.stat-item {
    text-align: center;
}

.stat-item .stat-value {
    display: block;
    font-size: 1.8rem;
    font-weight: bold;
    color: var(--accent-color);
}

.stat-item .stat-label {
    font-size: 0.85rem;
    color: var(--text-secondary);
}

.reset-btn {
    display: block;
    margin: 0 auto;
    padding: 10px 25px;
    border: 1px solid var(--danger-color);
    background: transparent;
    color: var(--danger-color);
    border-radius: 6px;
    cursor: pointer;
    font-size: 0.9rem;
    transition: all 0.2s ease;
}

.reset-btn:hover {
    background: var(--danger-color);
    color: white;
}

/* Footer */
footer {
    text-align: center;
    padding: 25px 0;
    margin-top: auto;
    border-top: 1px solid var(--border-color);
}

footer p {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

footer a {
    color: var(--primary-color);
    text-decoration: none;
    font-weight: 500;
    transition: color 0.2s ease;
}

footer a:hover {
    color: var(--secondary-color);
}

/* Mobile Responsive */
@media (max-width: 768px) {
    header h1 {
        font-size: 1.8rem;
    }

    .tagline {
        font-size: 0.95rem;
    }

    .mode-selection {
        flex-direction: column;
        align-items: stretch;
    }

    .mode-btn {
        width: 100%;
    }

    .settings-panel {
        flex-direction: column;
        align-items: stretch;
    }

    .setting-group select {
        width: 100%;
    }

    .score-display {
        grid-template-columns: repeat(2, 1fr);
    }

    .play-controls {
        flex-direction: column;
        align-items: stretch;
    }

    .play-btn, .replay-btn {
        justify-content: center;
    }

    .interval-buttons {
        grid-template-columns: repeat(2, 1fr);
    }

    .piano-keyboard {
        overflow-x: auto;
        justify-content: flex-start;
        padding: 0 10px;
    }

    .piano-key.white {
        width: 35px;
        height: 120px;
    }

    .piano-key.black {
        width: 24px;
        height: 75px;
    }

    .stats-grid {
        grid-template-columns: 1fr;
        gap: 10px;
    }
}

@media (max-width: 480px) {
    .app-container {
        padding: 15px;
    }

    header {
        padding: 20px 0;
    }

    header h1 {
        font-size: 1.5rem;
    }

    .interval-training, .melody-training, .statistics {
        padding: 15px;
    }

    .interval-btn {
        padding: 12px 8px;
        font-size: 0.85rem;
    }

    .progress-dot {
        width: 35px;
        height: 35px;
        font-size: 0.7rem;
    }
}

/* Audio visualization (optional enhancement) */
.playing {
    animation: pulse 0.5s ease infinite;
}

@keyframes pulse {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.05); }
}