:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --secondary-color: #64748b;
    --success-color: #10b981;
    --warning-color: #f59e0b;
    --danger-color: #ef4444;
    --signal-input: #3b82f6;
    --signal-kernel: #ef4444;
    --signal-output: #10b981;
    --signal-product: #a855f7;
    --signal-overlap: #f59e0b;
    --bg-color: #0f172a;
    --panel-bg: #1e293b;
    --border-color: #334155;
    --text-primary: #f1f5f9;
    --text-secondary: #94a3b8;
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.4);
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background: var(--bg-color);
    color: var(--text-primary);
    line-height: 1.6;
    padding: 20px;
    min-height: 100vh;
}

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

/* Header */
header {
    text-align: center;
    margin-bottom: 30px;
    padding: 20px;
    background: var(--panel-bg);
    border-radius: 12px;
    box-shadow: var(--shadow);
}

header h1 {
    font-size: 2rem;
    margin-bottom: 10px;
    color: var(--primary-color);
}

.subtitle {
    color: var(--text-secondary);
    font-size: 1rem;
    max-width: 800px;
    margin: 0 auto;
}

/* Formula Display */
.formulas {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 15px;
    margin-bottom: 30px;
}

.formula-item {
    background: var(--panel-bg);
    padding: 15px 20px;
    border-radius: 8px;
    border-left: 4px solid var(--primary-color);
    box-shadow: var(--shadow);
}

.formula-label {
    font-weight: 600;
    color: var(--text-secondary);
    font-size: 0.9rem;
    display: block;
    margin-bottom: 5px;
}

.formula-content {
    font-size: 1.1rem;
    color: var(--text-primary);
    font-family: 'Times New Roman', serif;
}

/* Visualization Container */
.visualization-container {
    background: var(--panel-bg);
    border-radius: 12px;
    padding: 25px;
    margin-bottom: 25px;
    box-shadow: var(--shadow-lg);
}

.domain-view {
    animation: fadeIn 0.3s ease-in-out;
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

.domain-title {
    text-align: center;
    margin-bottom: 20px;
    color: var(--primary-color);
    font-size: 1.3rem;
}

/* Signal Panels */
.signal-panel {
    background: var(--bg-color);
    border-radius: 8px;
    padding: 15px;
    margin-bottom: 15px;
    box-shadow: var(--shadow);
}

.panel-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 10px;
    flex-wrap: wrap;
    gap: 10px;
}

.panel-label {
    font-weight: 600;
    color: var(--text-primary);
    font-size: 1rem;
}

.panel-formula {
    font-family: 'Times New Roman', serif;
    color: var(--signal-overlap);
    font-size: 1.1rem;
}

.signal-canvas {
    width: 100%;
    height: 120px;
    background: #0a0f1e;
    border-radius: 6px;
    border: 1px solid var(--border-color);
}

.output-panel {
    border: 2px solid var(--signal-output);
}

/* FFT Grid */
.fft-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
    gap: 15px;
    align-items: center;
    justify-items: center;
}

.fft-panel {
    width: 100%;
}

.fft-multiply {
    font-size: 2rem;
    color: var(--text-secondary);
    font-weight: bold;
}

/* Metrics Panel */
.metrics-panel {
    background: var(--panel-bg);
    border-radius: 12px;
    padding: 20px;
    margin-bottom: 25px;
    box-shadow: var(--shadow);
}

.metrics-panel h3 {
    margin-bottom: 15px;
    color: var(--primary-color);
}

.metrics-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 15px;
    margin-bottom: 15px;
}

.metric-item {
    background: var(--bg-color);
    padding: 12px;
    border-radius: 6px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.metric-label {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.metric-value {
    color: var(--signal-output);
    font-weight: bold;
    font-size: 1.1rem;
    font-family: 'Courier New', monospace;
}

.calculation-detail {
    background: var(--bg-color);
    padding: 12px;
    border-radius: 6px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 10px;
}

.calc-label {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.calc-value {
    color: var(--signal-product);
    font-weight: bold;
    font-family: 'Courier New', monospace;
    font-size: 1rem;
    word-break: break-all;
}

/* Controls Panel */
.controls-panel {
    background: var(--panel-bg);
    border-radius: 12px;
    padding: 20px;
    margin-bottom: 25px;
    box-shadow: var(--shadow);
}

.controls-panel h3 {
    margin-bottom: 20px;
    color: var(--primary-color);
}

.control-group {
    margin-bottom: 20px;
}

.control-label {
    display: block;
    margin-bottom: 8px;
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: 500;
}

.btn {
    padding: 10px 20px;
    border: none;
    border-radius: 6px;
    font-size: 0.95rem;
    cursor: pointer;
    transition: all 0.2s ease;
    font-weight: 500;
    margin-right: 10px;
    margin-bottom: 10px;
}

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

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

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

.btn-secondary:hover {
    background: #475569;
    transform: translateY(-1px);
}

.slider-group {
    display: flex;
    align-items: center;
    gap: 15px;
    flex-wrap: wrap;
}

.slider {
    flex: 1;
    min-width: 200px;
    height: 6px;
    -webkit-appearance: none;
    appearance: none;
    background: var(--border-color);
    border-radius: 3px;
    outline: none;
}

.slider::-webkit-slider-thumb {
    -webkit-appearance: none;
    appearance: none;
    width: 18px;
    height: 18px;
    background: var(--primary-color);
    border-radius: 50%;
    cursor: pointer;
    transition: background 0.2s;
}

.slider::-webkit-slider-thumb:hover {
    background: var(--primary-hover);
}

.slider::-moz-range-thumb {
    width: 18px;
    height: 18px;
    background: var(--primary-color);
    border: none;
    border-radius: 50%;
    cursor: pointer;
}

.slider-value {
    min-width: 40px;
    text-align: center;
    color: var(--primary-color);
    font-weight: bold;
    font-family: 'Courier New', monospace;
}

.domain-toggle {
    display: flex;
    gap: 10px;
}

.domain-btn {
    padding: 10px 25px;
    background: var(--bg-color);
    color: var(--text-secondary);
    border: 2px solid var(--border-color);
    border-radius: 6px;
    cursor: pointer;
    transition: all 0.2s ease;
    font-weight: 500;
}

.domain-btn:hover {
    border-color: var(--primary-color);
    color: var(--primary-color);
}

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

/* Config Panel */
.config-panel {
    background: var(--panel-bg);
    border-radius: 12px;
    padding: 20px;
    margin-bottom: 25px;
    box-shadow: var(--shadow);
}

.config-panel h3 {
    margin-bottom: 20px;
    color: var(--primary-color);
}

.config-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 15px;
}

.config-item {
    display: flex;
    flex-direction: column;
}

.config-label {
    color: var(--text-secondary);
    font-size: 0.9rem;
    margin-bottom: 8px;
    font-weight: 500;
}

.config-select {
    padding: 10px;
    background: var(--bg-color);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
    border-radius: 6px;
    font-size: 0.95rem;
    cursor: pointer;
    outline: none;
}

.config-select:focus {
    border-color: var(--primary-color);
}

.config-label input[type="checkbox"] {
    margin-right: 8px;
    cursor: pointer;
}

/* Education Panel */
.education-panel {
    background: var(--panel-bg);
    border-radius: 12px;
    padding: 20px;
    margin-bottom: 25px;
    box-shadow: var(--shadow);
}

.education-panel h3 {
    margin-bottom: 20px;
    color: var(--primary-color);
}

.steps-container {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 15px;
    margin-bottom: 25px;
}

.step-card {
    background: var(--bg-color);
    padding: 15px;
    border-radius: 8px;
    border-left: 4px solid var(--signal-product);
}

.step-card h4 {
    color: var(--signal-product);
    margin-bottom: 8px;
    font-size: 1rem;
}

.step-card p {
    color: var(--text-secondary);
    font-size: 0.9rem;
    line-height: 1.5;
}

.concepts-container,
.applications-container {
    margin-top: 20px;
}

.concepts-container h4,
.applications-container h4 {
    color: var(--primary-color);
    margin-bottom: 12px;
}

.concept-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 12px;
}

.concept-item {
    background: var(--bg-color);
    padding: 12px;
    border-radius: 6px;
    font-size: 0.9rem;
}

.concept-item strong {
    color: var(--signal-overlap);
    display: block;
    margin-bottom: 4px;
}

.concept-item span {
    color: var(--text-secondary);
}

.applications-container ul {
    list-style: none;
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 10px;
}

.applications-container li {
    background: var(--bg-color);
    padding: 10px 15px;
    border-radius: 6px;
    color: var(--text-secondary);
    font-size: 0.9rem;
    position: relative;
    padding-left: 25px;
}

.applications-container li::before {
    content: "→";
    position: absolute;
    left: 10px;
    color: var(--signal-output);
}

/* Custom Draw Panel */
.custom-draw-panel {
    background: var(--panel-bg);
    border-radius: 12px;
    padding: 20px;
    margin-bottom: 25px;
    box-shadow: var(--shadow);
}

.custom-draw-panel h3 {
    margin-bottom: 10px;
    color: var(--primary-color);
}

.custom-draw-panel p {
    color: var(--text-secondary);
    margin-bottom: 15px;
}

.custom-canvas {
    width: 100%;
    height: 200px;
    background: #0a0f1e;
    border: 2px solid var(--primary-color);
    border-radius: 6px;
    cursor: crosshair;
    margin-bottom: 15px;
}

/* Responsive Design */
@media (max-width: 768px) {
    body {
        padding: 10px;
    }

    header h1 {
        font-size: 1.5rem;
    }

    .formulas {
        grid-template-columns: 1fr;
    }

    .signal-canvas {
        height: 100px;
    }

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

    .config-grid {
        grid-template-columns: 1fr;
    }

    .steps-container {
        grid-template-columns: 1fr;
    }

    .concept-grid,
    .applications-container ul {
        grid-template-columns: 1fr;
    }

    .btn {
        width: 100%;
        margin-right: 0;
    }

    .slider-group {
        flex-direction: column;
        align-items: stretch;
    }

    .slider {
        min-width: 100%;
    }
}

/* Animation State */
.playing .btn-primary {
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0%, 100% { opacity: 1; }
    50% { opacity: 0.7; }
}