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

:root {
    --color-primary: #2563eb;
    --color-primary-dark: #1d4ed8;
    --color-secondary: #10b981;
    --color-accent: #f59e0b;
    --color-danger: #ef4444;
    --color-success: #22c55e;
    --color-text: #1f2937;
    --color-text-light: #6b7280;
    --color-bg: #f9fafb;
    --color-card: #ffffff;
    --color-border: #e5e7eb;
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --font-size-xs: 0.75rem;
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.25rem;
    --font-size-2xl: 1.5rem;
}

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

.container {
    max-width: 1400px;
    margin: 0 auto;
    padding: 1rem;
}

/* Header */
header {
    text-align: center;
    margin-bottom: 2rem;
    padding: 2rem 0;
    background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-primary-dark) 100%);
    color: white;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
}

header h1 {
    font-size: var(--font-size-2xl);
    font-weight: 700;
    margin-bottom: 0.5rem;
}

.subtitle {
    font-size: var(--font-size-base);
    opacity: 0.95;
}

/* Main Content */
main {
    display: grid;
    grid-template-columns: 350px 1fr;
    gap: 2rem;
}

@media (max-width: 1024px) {
    main {
        grid-template-columns: 1fr;
    }
}

/* Controls Section */
.controls-section {
    background: var(--color-card);
    padding: 1.5rem;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
    height: fit-content;
}

.controls-section h2 {
    font-size: var(--font-size-xl);
    margin-bottom: 1rem;
    color: var(--color-primary);
}

.control-group {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.control-item {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.control-item label {
    font-size: var(--font-size-sm);
    font-weight: 500;
    color: var(--color-text-light);
}

.control-item input[type="range"] {
    width: 100%;
    height: 0.5rem;
    border-radius: var(--radius-sm);
    background: var(--color-border);
    outline: none;
    -webkit-appearance: none;
}

.control-item input[type="range"]::-webkit-slider-thumb {
    -webkit-appearance: none;
    appearance: none;
    width: 1rem;
    height: 1rem;
    border-radius: 50%;
    background: var(--color-primary);
    cursor: pointer;
    transition: background 0.2s;
}

.control-item input[type="range"]::-webkit-slider-thumb:hover {
    background: var(--color-primary-dark);
}

.control-item input[type="range"]::-moz-range-thumb {
    width: 1rem;
    height: 1rem;
    border-radius: 50%;
    background: var(--color-primary);
    cursor: pointer;
    border: none;
}

.value-display {
    font-size: var(--font-size-sm);
    font-weight: 600;
    color: var(--color-primary);
    text-align: right;
}

.control-item select {
    padding: 0.5rem;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    font-size: var(--font-size-sm);
    background: var(--color-bg);
    cursor: pointer;
    transition: border-color 0.2s;
}

.control-item select:hover,
.control-item select:focus {
    border-color: var(--color-primary);
    outline: none;
}

.button-group {
    display: flex;
    gap: 0.5rem;
    margin-top: 1rem;
}

button {
    padding: 0.625rem 1rem;
    border: none;
    border-radius: var(--radius-sm);
    font-size: var(--font-size-sm);
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s;
}

.btn-primary {
    background: var(--color-primary);
    color: white;
    flex: 1;
}

.btn-primary:hover {
    background: var(--color-primary-dark);
    transform: translateY(-1px);
}

.btn-secondary {
    background: var(--color-text-light);
    color: white;
    flex: 1;
}

.btn-secondary:hover {
    background: var(--color-text);
    transform: translateY(-1px);
}

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

.presets h3 {
    font-size: var(--font-size-base);
    margin-bottom: 0.75rem;
    color: var(--color-text);
}

.preset-buttons {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 0.5rem;
}

.preset-btn {
    background: var(--color-bg);
    color: var(--color-text);
    border: 1px solid var(--color-border);
    padding: 0.5rem;
    font-size: var(--font-size-xs);
}

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

/* Visualization Section */
.visualization-section {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.nyquist-indicator {
    background: var(--color-card);
    padding: 1.5rem;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
}

.nyquist-label {
    font-size: var(--font-size-sm);
    font-weight: 600;
    margin-bottom: 0.75rem;
    color: var(--color-text-light);
    text-align: center;
}

.nyquist-bar-container {
    position: relative;
    height: 2rem;
    margin-bottom: 0.75rem;
}

.nyquist-bar {
    width: 100%;
    height: 100%;
    background: var(--color-bg);
    border-radius: var(--radius-sm);
    overflow: hidden;
    position: relative;
}

.nyquist-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--color-success) 0%, var(--color-success) 100%);
    transition: width 0.3s ease, background 0.3s ease;
}

.nyquist-fill.warning {
    background: linear-gradient(90deg, var(--color-accent) 0%, var(--color-accent) 100%);
}

.nyquist-fill.danger {
    background: linear-gradient(90deg, var(--color-danger) 0%, var(--color-danger) 100%);
}

.nyquist-threshold {
    position: absolute;
    left: 50%;
    top: 0;
    bottom: 0;
    width: 2px;
    background: var(--color-text);
    z-index: 10;
}

.nyquist-threshold::after {
    content: '1.0';
    position: absolute;
    left: 50%;
    transform: translateX(-50%);
    top: -1.25rem;
    font-size: var(--font-size-xs);
    font-weight: 600;
    color: var(--color-text);
}

.nyquist-value {
    text-align: center;
    font-size: var(--font-size-xl);
    font-weight: 700;
    color: var(--color-primary);
    margin-bottom: 0.5rem;
}

.nyquist-status {
    text-align: center;
    font-size: var(--font-size-sm);
    font-weight: 600;
    padding: 0.5rem;
    border-radius: var(--radius-sm);
    background: var(--color-success);
    color: white;
    transition: background 0.3s ease;
}

.nyquist-status.warning {
    background: var(--color-accent);
}

.nyquist-status.danger {
    background: var(--color-danger);
}

/* Canvas Containers */
.canvas-container,
.spectrum-container {
    background: var(--color-card);
    padding: 1rem;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
}

.canvas-container canvas,
.spectrum-container canvas {
    width: 100%;
    height: auto;
    display: block;
}

.canvas-legend,
.spectrum-legend {
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;
    justify-content: center;
    margin-top: 0.75rem;
    padding-top: 0.75rem;
    border-top: 1px solid var(--color-border);
}

.legend-item {
    display: flex;
    align-items: center;
    gap: 0.375rem;
    font-size: var(--font-size-xs);
}

.legend-color {
    width: 1rem;
    height: 1rem;
    border-radius: var(--radius-sm);
    flex-shrink: 0;
}

.legend-color.original {
    background: #2563eb;
}

.legend-color.samples {
    background: #dc2626;
    border-radius: 50%;
}

.legend-color.reconstructed {
    background: #10b981;
}

.legend-color.aliased {
    background: #f59e0b;
}

/* Metrics Panel */
.metrics-panel {
    background: var(--color-card);
    padding: 1.5rem;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1rem;
}

.metric-item {
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
}

.metric-label {
    font-size: var(--font-size-xs);
    color: var(--color-text-light);
    font-weight: 500;
}

.metric-value {
    font-size: var(--font-size-lg);
    font-weight: 600;
    color: var(--color-primary);
}

/* Education Section */
.education-section {
    background: var(--color-card);
    padding: 2rem;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
    margin-top: 2rem;
    width: 100%;
    max-width: 100%;
}

.education-section h2 {
    font-size: var(--font-size-xl);
    margin-bottom: 1.5rem;
    color: var(--color-primary);
}

.concept-tabs {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 1.5rem;
    flex-wrap: wrap;
}

.tab-btn {
    padding: 0.625rem 1rem;
    background: var(--color-bg);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    font-size: var(--font-size-sm);
    cursor: pointer;
    transition: all 0.2s;
}

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

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

.tab-content {
    display: none;
}

.tab-content.active {
    display: block;
    animation: fadeIn 0.3s ease;
}

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

.tab-content h3 {
    font-size: var(--font-size-lg);
    margin-bottom: 1rem;
    color: var(--color-text);
}

.tab-content h4 {
    font-size: var(--font-size-base);
    margin-bottom: 0.75rem;
    color: var(--color-primary);
}

.tab-content p {
    margin-bottom: 1rem;
    line-height: 1.8;
}

.formula-box {
    background: var(--color-bg);
    padding: 1rem;
    border-radius: var(--radius-md);
    margin: 1rem 0;
    border-left: 3px solid var(--color-primary);
}

.formula-box h4 {
    font-size: var(--font-size-sm);
    margin-bottom: 0.5rem;
}

.formula {
    font-size: 1.1rem;
    overflow-x: auto;
    padding: 0.5rem;
}

.key-points {
    list-style: none;
    padding: 0;
}

.key-points li {
    padding: 0.5rem 0;
    padding-left: 1.5rem;
    position: relative;
}

.key-points li::before {
    content: '•';
    position: absolute;
    left: 0;
    color: var(--color-primary);
    font-weight: 700;
}

.examples-list {
    list-style: none;
    padding: 0;
    margin: 1rem 0;
}

.examples-list li {
    padding: 0.75rem;
    background: var(--color-bg);
    border-radius: var(--radius-sm);
    margin-bottom: 0.5rem;
    border-left: 3px solid var(--color-accent);
}

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

.method-card {
    background: var(--color-bg);
    padding: 1rem;
    border-radius: var(--radius-md);
    border-top: 3px solid var(--color-secondary);
}

.method-card h4 {
    font-size: var(--font-size-base);
    margin-bottom: 0.5rem;
}

.method-card p {
    font-size: var(--font-size-sm);
    margin-bottom: 0.5rem;
}

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

.application-card {
    background: var(--color-bg);
    padding: 1rem;
    border-radius: var(--radius-md);
    border-top: 3px solid var(--color-accent);
}

.application-card h4 {
    font-size: var(--font-size-base);
    margin-bottom: 0.5rem;
}

.application-card p {
    font-size: var(--font-size-sm);
}

/* Footer */
footer {
    text-align: center;
    margin-top: 3rem;
    padding: 1.5rem;
    color: var(--color-text-light);
    font-size: var(--font-size-sm);
    border-top: 1px solid var(--color-border);
}

/* Responsive Design */
@media (max-width: 768px) {
    .container {
        padding: 0.5rem;
    }

    header h1 {
        font-size: var(--font-size-xl);
    }

    .subtitle {
        font-size: var(--font-size-sm);
    }

    .controls-section {
        padding: 1rem;
    }

    .preset-buttons {
        grid-template-columns: 1fr;
    }

    .metrics-panel {
        grid-template-columns: 1fr;
    }

    .concept-tabs {
        flex-direction: column;
    }

    .tab-btn {
        width: 100%;
    }

    .method-cards,
    .application-grid {
        grid-template-columns: 1fr;
    }
}