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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background: var(--bg-color);
    transition: background-color 0.3s ease, color 0.3s ease;
}

:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --success-color: #059669;
    --success-bg: #ecfdf5;
    --danger-color: #dc2626;
    --danger-bg: #fef2f2;
    --warning-color: #d97706;
    --warning-bg: #fef3c7;
    --info-color: #0891b2;
    --info-bg: #cffafe;
    --excellent-color: #059669;
    --good-color: #0891b2;
    --satisfactory-color: #d97706;
    --needs-improvement-color: #dc2626;
    --failing-color: #7c2d12;
    --bg-color: #ffffff;
    --card-bg: #f8fafc;
    --text-color: #1f2937;
    --text-muted: #6b7280;
    --border-color: #e5e7eb;
    --border-radius: 12px;
    --shadow: 0 1px 3px 0 rgba(0, 0, 0, 0.1), 0 1px 2px 0 rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
}

@media (prefers-color-scheme: dark) {
    :root {
        --bg-color: #111827;
        --card-bg: #1f2937;
        --text-color: #f3f4f6;
        --text-muted: #9ca3af;
        --border-color: #374151;
        --success-bg: #064e3b;
        --danger-bg: #7f1d1d;
        --warning-bg: #451a03;
        --info-bg: #0c4a6e;
    }
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem 1rem;
}

header {
    text-align: center;
    margin-bottom: 3rem;
}

h1 {
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--primary-color);
    margin-bottom: 0.5rem;
}

header p {
    font-size: 1.1rem;
    color: var(--text-muted);
    max-width: 600px;
    margin: 0 auto;
}

.input-section {
    background: var(--card-bg);
    border-radius: var(--border-radius);
    padding: 2rem;
    margin-bottom: 2rem;
    box-shadow: var(--shadow);
    border: 1px solid var(--border-color);
}

.input-section h2 {
    font-size: 1.5rem;
    font-weight: 600;
    margin-bottom: 1.5rem;
    color: var(--text-color);
}

.input-tabs {
    display: flex;
    border-bottom: 1px solid var(--border-color);
    margin-bottom: 1.5rem;
    overflow-x: auto;
}

.tab-button {
    background: none;
    border: none;
    padding: 1rem 1.5rem;
    cursor: pointer;
    font-size: 0.9rem;
    font-weight: 500;
    color: var(--text-muted);
    border-bottom: 2px solid transparent;
    transition: all 0.2s ease;
    white-space: nowrap;
}

.tab-button.active {
    color: var(--primary-color);
    border-bottom-color: var(--primary-color);
}

.tab-button:hover {
    color: var(--primary-color);
}

.tab-content {
    display: none;
}

.tab-content.active {
    display: block;
}

.input-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1.5rem;
    margin-bottom: 1.5rem;
}

.input-group {
    display: flex;
    flex-direction: column;
}

.input-group.full-width {
    grid-column: 1 / -1;
}

label {
    font-weight: 500;
    margin-bottom: 0.5rem;
    color: var(--text-color);
    font-size: 0.9rem;
}

input, select, textarea {
    padding: 0.75rem 1rem;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    font-size: 1rem;
    background: var(--bg-color);
    color: var(--text-color);
    transition: border-color 0.2s ease, box-shadow 0.2s ease;
    resize: vertical;
}

input:focus, select:focus, textarea:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

input[type="file"] {
    border: 2px dashed var(--border-color);
    padding: 2rem;
    text-align: center;
    cursor: pointer;
}

input[type="file"]:hover {
    border-color: var(--primary-color);
}

.file-info {
    margin-top: 0.5rem;
}

.file-info small {
    color: var(--text-muted);
    font-size: 0.8rem;
}

.settings-section {
    margin-top: 2rem;
    padding-top: 1.5rem;
    border-top: 1px solid var(--border-color);
}

button {
    background: var(--primary-color);
    color: white;
    border: none;
    padding: 0.875rem 1.5rem;
    border-radius: 8px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
    box-shadow: var(--shadow);
}

button:hover {
    background: var(--primary-hover);
    transform: translateY(-1px);
    box-shadow: var(--shadow-lg);
}

button:active {
    transform: translateY(0);
}

.results-section {
    display: none;
}

.results-section.show {
    display: block;
    animation: slideIn 0.3s ease;
}

.results-section h2 {
    font-size: 2rem;
    font-weight: 700;
    color: var(--text-color);
    margin-bottom: 2rem;
    text-align: center;
}

.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 1.5rem;
    margin-bottom: 3rem;
}

.stat-card {
    background: var(--card-bg);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    box-shadow: var(--shadow);
    border: 1px solid var(--border-color);
}

.stat-card h3 {
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--text-color);
    margin-bottom: 1rem;
    text-align: center;
}

.stat-items {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.stat-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.5rem 0;
    border-bottom: 1px solid var(--border-color);
}

.stat-item:last-child {
    border-bottom: none;
}

.stat-item span {
    color: var(--text-muted);
    font-size: 0.9rem;
}

.stat-item strong {
    color: var(--text-color);
    font-size: 1rem;
}

.stat-item.success strong {
    color: var(--success-color);
}

.stat-item.danger strong {
    color: var(--danger-color);
}

.stat-item.excellent strong {
    color: var(--excellent-color);
}

.stat-item.good strong {
    color: var(--good-color);
}

.stat-item.satisfactory strong {
    color: var(--satisfactory-color);
}

.stat-item.needs-improvement strong {
    color: var(--needs-improvement-color);
}

.stat-item.failing strong {
    color: var(--failing-color);
}

.chart-section {
    background: var(--card-bg);
    border-radius: var(--border-radius);
    padding: 2rem;
    margin-bottom: 2rem;
    box-shadow: var(--shadow);
    border: 1px solid var(--border-color);
    text-align: center;
}

.chart-section h3 {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--text-color);
    margin-bottom: 1.5rem;
}

.chart-container {
    position: relative;
    width: 100%;
    height: 400px;
}

#distribution-chart {
    max-width: 100%;
    height: auto;
}

.export-buttons {
    display: flex;
    gap: 1rem;
    justify-content: center;
    margin-bottom: 2rem;
}

.export-buttons button {
    background: var(--success-color);
}

.export-buttons button:hover {
    background: #047857;
}

.action-buttons {
    text-align: center;
    margin-top: 2rem;
}

.clear-button {
    background: var(--danger-color);
    color: white;
}

.clear-button:hover {
    background: #b91c1c;
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateY(-20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@media (max-width: 768px) {
    .container {
        padding: 1rem;
    }

    h1 {
        font-size: 2rem;
    }

    .input-section {
        padding: 1.5rem;
    }

    .input-grid {
        grid-template-columns: 1fr;
        gap: 1rem;
    }

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

    .chart-section {
        padding: 1.5rem;
    }

    .export-buttons {
        flex-direction: column;
        align-items: center;
    }

    .export-buttons button {
        width: 200px;
    }

    .tab-button {
        padding: 0.75rem 1rem;
        font-size: 0.85rem;
    }
}