:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --secondary-color: #f8fafc;
    --accent-color: #10b981;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --border-color: #e2e8f0;
    --card-bg: #ffffff;
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
    --radius: 0.5rem;
    --radius-lg: 0.75rem;
    --spacing-xs: 0.5rem;
    --spacing-sm: 0.75rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
}

* {
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background: linear-gradient(135deg, #f1f5f9 0%, #e2e8f0 100%);
    color: var(--text-primary);
    margin: 0;
    padding: 0;
    line-height: 1.6;
    transition: all 0.3s ease;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: var(--spacing-xl);
    padding-bottom: 120px; /* Space for fixed action buttons */
    min-height: 100vh;
}

.header {
    background: var(--card-bg);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
    margin-bottom: var(--spacing-xl);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-md);
}

#logo {
    width: 80px;
    height: 80px;
    object-fit: contain;
    border-radius: var(--radius);
    box-shadow: var(--shadow-sm);
}

.header h1 {
    font-size: 2rem;
    font-weight: 700;
    margin: 0;
    color: var(--text-primary);
    text-align: center;
}

.content {
    display: grid;
    gap: var(--spacing-xl);
}

.intro-section {
    text-align: center;
    background: var(--card-bg);
    padding: var(--spacing-xl);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
}

.intro-section p {
    font-size: 1.1rem;
    color: var(--text-secondary);
    margin: 0 0 var(--spacing-lg) 0;
}

.intro-section a {
    color: var(--primary-color);
    text-decoration: none;
    font-weight: 600;
    transition: color 0.2s ease;
}

.intro-section a:hover {
    color: var(--primary-hover);
}

.form-grid {
    display: grid;
    gap: var(--spacing-xl);
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    margin: var(--spacing-md) 0;
}

.controls {
    background: var(--card-bg);
    padding: var(--spacing-xl);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
    border: 1px solid var(--border-color);
    margin: var(--spacing-xl) 0;
}

.controls h3 {
    margin: 0 0 var(--spacing-md) 0;
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--text-primary);
    padding-bottom: var(--spacing-sm);
    border-bottom: 2px solid var(--border-color);
}

.controls.flex-row {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-md);
    align-items: center;
}

.controls.flex-row label {
    flex: 1;
    min-width: 140px;
    margin: 0;
}

.form-group {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xs);
}

.form-group label {
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-xs);
}

.checkbox-group {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: var(--spacing-sm);
    margin-top: var(--spacing-sm);
}

/* Specific 4-column layout for Available Notes section */
.controls:has(.notelist) .checkbox-group {
    grid-template-columns: repeat(4, 1fr);
}

.checkbox-item {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
    padding: var(--spacing-xs);
    border-radius: var(--radius);
    transition: background-color 0.2s ease;
}

.checkbox-item:hover {
    background-color: var(--secondary-color);
}

.checkbox-item input[type="checkbox"] {
    width: 18px;
    height: 18px;
    accent-color: var(--primary-color);
}

.checkbox-item label {
    font-size: 0.9rem;
    margin: 0;
    cursor: pointer;
    color: var(--text-primary);
}

.button-group {
    display: flex;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-md);
    flex-wrap: wrap;
}

.btn {
    padding: var(--spacing-sm) var(--spacing-md);
    border: none;
    border-radius: var(--radius);
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
    text-decoration: none;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-xs);
}

.btn-primary {
    background: var(--primary-color);
    color: white;
    box-shadow: var(--shadow-sm);
}

.btn-primary:hover {
    background: var(--primary-hover);
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

.btn-secondary {
    background: var(--secondary-color);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
}

.btn-secondary:hover {
    background: #e2e8f0;
    transform: translateY(-1px);
}

.btn-success {
    background: var(--accent-color);
    color: white;
    box-shadow: var(--shadow-sm);
}

.btn-success:hover {
    background: #059669;
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

button, input[type="submit"], input[type="button"], select, input[type="number"] {
    padding: var(--spacing-sm) var(--spacing-md);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    font-size: 0.9rem;
    font-weight: 500;
    background: white;
    color: var(--text-primary);
    cursor: pointer;
    transition: all 0.2s ease;
}

button:hover, input[type="submit"]:hover, input[type="button"]:hover, select:hover, input[type="number"]:hover {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgb(37 99 235 / 0.1);
}

input[type="submit"] {
    font-size: 1.1rem;
    padding: var(--spacing-md) var(--spacing-xl);
    font-weight: 700;
}

.action-buttons {
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    z-index: 999;
    display: flex;
    gap: var(--spacing-md);
    justify-content: center;
    align-items: center;
    flex-wrap: wrap;
    background: var(--card-bg);
    padding: var(--spacing-lg);
    border-top: 1px solid var(--border-color);
    box-shadow: 0 -4px 20px rgba(0, 0, 0, 0.1);
    backdrop-filter: blur(10px);
}

.instrument-selector {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    color: var(--text-secondary);
    font-size: 0.9rem;
}



.metronome-row {
    display: flex;
    gap: var(--spacing-md);
    align-items: center;
    justify-content: center;
    margin-bottom: var(--spacing-lg);
    flex-wrap: wrap;
}

.metronome-row .form-group {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
    margin: 0;
}

.metronome-row .form-group label {
    margin: 0;
    white-space: nowrap;
}

.time-limit-buttons {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(80px, 1fr));
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-lg);
}

.time-limit-buttons button {
    padding: var(--spacing-sm);
    font-size: 0.85rem;
    border-radius: var(--radius);
}

#countdown-timer {
    font-size: 1.5rem;
    font-weight: 700;
    font-family: 'SF Mono', 'Monaco', 'Inconsolata', 'Roboto Mono', monospace;
    text-align: center;
    padding: var(--spacing-md);
    background: linear-gradient(135deg, #1e293b, #334155);
    color: white;
    border-radius: var(--radius);
    box-shadow: var(--shadow-md);
    letter-spacing: 0.1em;
    text-shadow: 0 0 10px rgba(59, 130, 246, 0.5);
}

#paper {
    background: white;
    padding: var(--spacing-xl);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-lg);
    border: 1px solid var(--border-color);
    overflow-x: auto;
    min-height: 200px;
    margin: var(--spacing-xl) 0;
}

#dark-mode-toggle {
    position: fixed;
    top: var(--spacing-lg);
    right: var(--spacing-lg);
    z-index: 1000;
    border-radius: 50px;
    padding: var(--spacing-sm) var(--spacing-md);
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    box-shadow: var(--shadow-md);
    font-size: 0.9rem;
    font-weight: 600;
}

.error {
    color: #dc2626;
    background: #fef2f2;
    border: 1px solid #fecaca;
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--radius);
    font-size: 0.9rem;
    margin-top: var(--spacing-sm);
    display: none;
}

.notelist, .length-list, .rest-list {
    list-style: none;
    padding: 0;
    margin: 0;
    display: contents;
}

.notelist li, .length-list li, .rest-list li {
    display: contents;
}

/* Dark mode styles */
body.dark-mode {
    --card-bg: #1e293b;
    --text-primary: #f1f5f9;
    --text-secondary: #94a3b8;
    --border-color: #334155;
    --secondary-color: #334155;
    background: linear-gradient(135deg, #0f172a 0%, #1e293b 100%);
}

.dark-mode .controls,
.dark-mode .header,
.dark-mode .intro-section,
.dark-mode .action-buttons,
.dark-mode #paper {
    background: var(--card-bg);
    border-color: var(--border-color);
}

.dark-mode .action-buttons {
    border-top-color: var(--border-color);
    box-shadow: 0 -4px 20px rgba(0, 0, 0, 0.3);
}

.dark-mode .checkbox-item:hover {
    background-color: #334155;
}

.dark-mode .btn-secondary {
    background: var(--secondary-color);
    color: var(--text-primary);
}

.dark-mode .btn-secondary:hover {
    background: #475569;
}

.dark-mode button,
.dark-mode input[type="submit"],
.dark-mode input[type="button"],
.dark-mode select,
.dark-mode input[type="number"] {
    background: var(--card-bg);
    color: var(--text-primary);
    border-color: var(--border-color);
}

.dark-mode .error {
    color: #fca5a5;
    background: #7f1d1d;
    border-color: #991b1b;
}

.dark-mode a {
    color: #60a5fa;
}

.dark-mode a:hover {
    color: #93c5fd;
}

/* Challenge Mode Styles */
.challenge-stats {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: var(--spacing-sm);
    margin: var(--spacing-md) 0;
    padding: var(--spacing-sm);
    background: var(--secondary-color);
    border-radius: var(--radius);
    font-weight: 600;
}

.challenge-answer {
    display: none;
    margin: var(--spacing-md) 0;
    padding: var(--spacing-md);
    background: var(--card-bg);
    border: 2px solid var(--primary-color);
    border-radius: var(--radius);
}

.challenge-question {
    font-size: 1.1rem;
    font-weight: 600;
    margin-bottom: var(--spacing-sm);
    color: var(--text-primary);
}

.answer-buttons {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(80px, 1fr));
    gap: var(--spacing-sm);
    margin: var(--spacing-sm) 0;
}

.answer-btn {
    padding: var(--spacing-sm);
    border: 1px solid var(--border-color);
    background: var(--card-bg);
    color: var(--text-primary);
    border-radius: var(--radius);
    cursor: pointer;
    transition: all 0.2s ease;
    font-weight: 500;
}

.answer-btn:hover {
    background: var(--primary-color);
    color: white;
}

.answer-btn.correct {
    background: var(--accent-color);
    color: white;
    border-color: var(--accent-color);
}

.answer-btn.incorrect {
    background: #dc2626;
    color: white;
    border-color: #dc2626;
}

.challenge-feedback {
    margin-top: var(--spacing-sm);
    padding: var(--spacing-sm);
    border-radius: var(--radius);
    font-weight: 600;
    text-align: center;
}

.challenge-feedback.correct {
    background: #dcfce7;
    color: #16a34a;
    border: 1px solid #bbf7d0;
}

.challenge-feedback.incorrect {
    background: #fef2f2;
    color: #dc2626;
    border: 1px solid #fecaca;
}

.dark-mode .challenge-stats {
    background: var(--secondary-color);
}

.dark-mode .challenge-feedback.correct {
    background: #14532d;
    color: #4ade80;
    border-color: #166534;
}

.dark-mode .challenge-feedback.incorrect {
    background: #7f1d1d;
    color: #fca5a5;
    border-color: #991b1b;
}

/* Playback Challenge Styles */
.playback-challenge {
    padding: var(--spacing-md);
    background: var(--secondary-color);
    border-radius: var(--radius);
    margin: var(--spacing-sm) 0;
}

.playback-challenge p {
    margin: var(--spacing-xs) 0;
    font-weight: 600;
}

#played-notes-display {
    color: var(--primary-color);
    font-family: monospace;
}

#pitch-feedback {
    margin: var(--spacing-sm) 0;
    font-size: 0.9rem;
}

.dark-mode .playback-challenge {
    background: var(--secondary-color);
}

/* Responsive design */
@media (max-width: 768px) {
    .container {
        padding: var(--spacing-sm);
        padding-bottom: 160px; /* More space for fixed buttons */
    }
    
    .header {
        flex-direction: column;
        text-align: center;
        padding: var(--spacing-md);
    }
    
    .header h2 {
        font-size: 1.5rem;
        margin: var(--spacing-sm) 0 0 0;
    }
    
    #logo {
        width: 60px;
        height: 60px;
    }
    
    .form-grid {
        grid-template-columns: 1fr;
        gap: var(--spacing-md);
    }
    
    .controls {
        padding: var(--spacing-md);
    }
    
    .controls.flex-row {
        flex-direction: column;
        gap: var(--spacing-sm);
    }
    
    .controls.flex-row label {
        width: 100%;
    }
    
    /* Better touch targets for mobile */
    .checkbox-item {
        padding: var(--spacing-sm);
        min-height: 44px; /* iOS recommended touch target */
        align-items: center;
    }
    
    .checkbox-item input[type="checkbox"] {
        width: 20px;
        height: 20px;
        margin-right: var(--spacing-sm);
    }
    
    .checkbox-item label {
        font-size: 1rem;
        line-height: 1.4;
    }
    
    /* Mobile-optimized button group */
    .button-group {
        display: grid;
        grid-template-columns: repeat(2, 1fr);
        gap: var(--spacing-xs);
        margin-bottom: var(--spacing-md);
    }
    
    .btn {
        padding: var(--spacing-sm) var(--spacing-xs);
        font-size: 0.85rem;
        min-height: 44px;
        white-space: nowrap;
    }
    
    /* Mobile action buttons */
    .action-buttons {
        flex-direction: column;
        gap: var(--spacing-sm);
        padding: var(--spacing-md);
        align-items: stretch;
    }
    
    .action-buttons .btn {
        width: 100%;
        justify-content: center;
        padding: var(--spacing-md);
        font-size: 1rem;
        min-height: 48px;
    }
    
    .instrument-selector {
        justify-content: center;
        margin-top: var(--spacing-sm);
    }
    
    /* Mobile form inputs */
    input[type="number"], select {
        padding: var(--spacing-sm);
        font-size: 1rem;
        min-height: 44px;
        width: 100%;
    }
    
    /* Mobile metronome */
    .metronome-row {
        flex-direction: column;
        gap: var(--spacing-sm);
        align-items: stretch;
    }
    
    .metronome-row .form-group {
        flex-direction: row;
        gap: var(--spacing-sm);
        align-items: center;
    }
    
    .metronome-row input {
        flex: 1;
    }
    
    .time-limit-buttons {
        grid-template-columns: repeat(2, 1fr);
        gap: var(--spacing-xs);
    }
    
    .time-limit-buttons button {
        min-height: 44px;
        font-size: 0.9rem;
    }
    
    /* Mobile paper/music display */
    #paper {
        margin: var(--spacing-md) 0;
        padding: var(--spacing-sm);
        overflow-x: auto;
        -webkit-overflow-scrolling: touch;
    }
    
    /* Dark mode toggle mobile positioning */
    #dark-mode-toggle {
        top: var(--spacing-sm);
        right: var(--spacing-sm);
        padding: var(--spacing-xs) var(--spacing-sm);
        font-size: 0.8rem;
    }
}

@media (max-width: 480px) {
    .container {
        padding: var(--spacing-xs);
        padding-bottom: 180px;
    }
    
    .header h2 {
        font-size: 1.25rem;
    }
    
    .controls h3 {
        font-size: 1.1rem;
    }
    
    /* Single column for very small screens */
    .checkbox-group {
        grid-template-columns: 1fr;
    }
    
    /* Stack buttons vertically on very small screens */
    .button-group {
        grid-template-columns: 1fr;
    }
    
    .time-limit-buttons {
        grid-template-columns: 1fr;
    }
    
    /* Larger touch targets for tiny screens */
    .checkbox-item {
        min-height: 48px;
        padding: var(--spacing-sm);
    }
    
    /* Mobile-first countdown timer */
    #countdown-timer {
        font-size: 1.25rem;
        padding: var(--spacing-sm);
    }
}

/* Touch-specific improvements */
@media (hover: none) and (pointer: coarse) {
    .checkbox-item:hover {
        background-color: transparent;
    }
    
    .checkbox-item:active {
        background-color: var(--secondary-color);
    }
    
    .btn:hover {
        transform: none;
    }
    
    .btn:active {
        transform: scale(0.98);
    }
}