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

:root {
    --primary: #1e40af;
    --primary-light: #3b82f6;
    --danger: #dc2626;
    --success: #10b981;
    --warning: #f59e0b;
    --bg: #f0f9ff;
    --card-bg: #fff;
    --text: #1f2937;
    --text-light: #6b7280;
    --border: #e5e7eb;
    --shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
    --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.12);
}

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

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* Header */
.header {
    background: linear-gradient(135deg, #1e40af 0%, #3b82f6 100%);
    color: white;
    padding: 60px 20px;
    text-align: center;
}

.header h1 {
    font-size: 2.5rem;
    margin-bottom: 12px;
    font-weight: 700;
}

.subtitle {
    font-size: 1.1rem;
    opacity: 0.95;
    font-weight: 300;
}

/* Main */
main {
    padding: 40px 0;
}

section {
    margin-bottom: 60px;
}

section h2 {
    font-size: 2rem;
    margin-bottom: 30px;
    color: var(--text);
    border-bottom: 3px solid var(--primary);
    padding-bottom: 12px;
    display: inline-block;
}

section h3 {
    font-size: 1.4rem;
    margin-top: 28px;
    margin-bottom: 16px;
    color: var(--primary);
    font-weight: 600;
}

section h4 {
    font-size: 1.1rem;
    margin-bottom: 12px;
    color: var(--text);
    font-weight: 600;
}

section p {
    font-size: 1rem;
    color: var(--text-light);
    margin-bottom: 16px;
    line-height: 1.8;
}

/* Intro */
.intro {
    margin-bottom: 40px;
}

/* Featured Tool */
.featured-tool {
    background: var(--card-bg);
    padding: 40px 20px;
    border-radius: 12px;
    box-shadow: var(--shadow-lg);
    margin-bottom: 40px;
    border-top: 4px solid var(--primary);
}

.featured-tool h2 {
    margin-bottom: 12px;
}

.featured-tool > .container > p {
    margin-bottom: 24px;
    color: var(--text-light);
}

/* Calculator */
.spreads-calc {
    margin-top: 20px;
}

.calc-section {
    margin-bottom: 30px;
    padding-bottom: 30px;
    border-bottom: 1px solid var(--border);
}

.calc-section:last-child {
    border-bottom: none;
    margin-bottom: 0;
    padding-bottom: 0;
}

.calc-section h3 {
    margin-top: 0;
}

.calc-section h4 {
    margin-top: 20px;
    margin-bottom: 12px;
}

.section-hint {
    font-size: 0.9rem;
    color: var(--text-light);
    margin-bottom: 12px;
}

/* Inputs */
.inputs-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 16px;
    margin-bottom: 20px;
}

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

.input-group label {
    font-size: 0.9rem;
    font-weight: 600;
    margin-bottom: 6px;
    color: var(--text);
}

.input-group input {
    padding: 10px 12px;
    border: 1px solid var(--border);
    border-radius: 6px;
    font-size: 1rem;
    transition: all 0.2s ease;
}

.input-group input:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(30, 64, 175, 0.1);
}

/* Spread Legs */
.spread-legs {
    background: #f9fafb;
    padding: 20px;
    border-radius: 8px;
    margin: 20px 0;
}

.spread-legs h4 {
    margin-top: 0;
    padding-bottom: 12px;
    border-bottom: 2px solid var(--border);
}

.spread-legs h4:not(:first-of-type) {
    margin-top: 20px;
}

/* Quick Scenarios */
.quick-scenarios {
    background: var(--card-bg);
    padding: 16px;
    border-radius: 8px;
    border: 1px solid var(--border);
    margin: 16px 0;
}

.template-label {
    font-size: 0.85rem;
    color: var(--text-light);
    font-weight: 600;
    margin-bottom: 10px;
}

.scenario-btn {
    padding: 8px 14px;
    background: #f3f4f6;
    color: var(--text);
    border: 1px solid var(--border);
    border-radius: 6px;
    font-size: 0.85rem;
    cursor: pointer;
    margin-right: 8px;
    margin-bottom: 8px;
    transition: all 0.2s ease;
}

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

/* Calculate Button */
.calculate-btn {
    width: 100%;
    padding: 14px;
    background: var(--primary);
    color: white;
    border: none;
    border-radius: 6px;
    font-size: 1.05rem;
    font-weight: 700;
    cursor: pointer;
    transition: all 0.3s ease;
    margin-top: 16px;
}

.calculate-btn:hover {
    background: var(--primary-light);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

/* Results */
.calc-results {
    background: #eff6ff;
    padding: 24px;
    border-radius: 8px;
    border: 2px solid var(--primary);
    margin-top: 20px;
}

.results-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
    gap: 16px;
    margin: 20px 0;
}

.result-card {
    background: white;
    padding: 16px;
    border-radius: 6px;
    border: 1px solid var(--border);
    text-align: center;
}

.metric-label {
    display: block;
    font-size: 0.8rem;
    color: var(--text-light);
    font-weight: 600;
    text-transform: uppercase;
    margin-bottom: 8px;
}

.metric-display {
    display: block;
    font-size: 1.6rem;
    font-weight: 700;
    color: var(--primary);
    margin-bottom: 4px;
}

.metric-display.green {
    color: var(--success);
}

.metric-display.danger {
    color: var(--danger);
}

.metric-hint {
    display: block;
    font-size: 0.75rem;
    color: var(--text-light);
    font-style: italic;
}

/* Metrics Grid */
.metrics-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 16px;
    margin: 20px 0;
}

.metric-box {
    background: white;
    padding: 16px;
    border-radius: 6px;
    border: 1px solid var(--border);
}

.metric-box h4 {
    margin-top: 0;
    margin-bottom: 8px;
}

.metric-box p {
    margin: 0;
    font-size: 0.9rem;
}

/* Chart Section */
.chart-section {
    background: white;
    padding: 20px;
    border-radius: 6px;
    border: 1px solid var(--border);
    margin: 20px 0;
}

.chart-section h4 {
    margin-top: 0;
}

/* Payoff Table */
.payoff-table {
    background: white;
    padding: 20px;
    border-radius: 6px;
    border: 1px solid var(--border);
    margin: 20px 0;
    overflow-x: auto;
}

.payoff-table h4 {
    margin-top: 0;
}

table {
    width: 100%;
    border-collapse: collapse;
}

thead {
    background: #f3f4f6;
    border-bottom: 2px solid var(--border);
}

th {
    padding: 12px;
    text-align: left;
    font-weight: 600;
    font-size: 0.9rem;
}

td {
    padding: 10px 12px;
    border-bottom: 1px solid var(--border);
    font-size: 0.9rem;
}

tbody tr:hover {
    background: #f9fafb;
}

.input-hint {
    display: block;
    font-size: 0.75rem;
    color: var(--text-light);
    font-style: italic;
    margin-top: 2px;
}

/* Greeks Section */
.greeks-section {
    background: white;
    padding: 20px;
    border-radius: 6px;
    border: 1px solid var(--border);
    margin: 20px 0;
}

.greeks-hint {
    font-size: 0.9rem;
    color: var(--text-light);
    margin-bottom: 16px;
}

.greeks-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
    gap: 16px;
}

.greek-card {
    background: linear-gradient(135deg, #f0f9ff 0%, #e0f2fe 100%);
    padding: 16px;
    border-radius: 6px;
    border: 1px solid var(--border);
    text-align: center;
}

.greek-label {
    display: block;
    font-size: 0.95rem;
    font-weight: 700;
    color: var(--primary);
    margin-bottom: 8px;
}

.greek-value {
    display: block;
    font-size: 1.4rem;
    font-weight: 700;
    color: var(--text);
    margin-bottom: 6px;
}

.greek-hint {
    display: block;
    font-size: 0.75rem;
    color: var(--text-light);
    line-height: 1.4;
}

/* Spread Metrics */
.spread-metrics {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 12px;
    margin: 12px 0;
}

.metric-small {
    display: flex;
    flex-direction: column;
    background: #f3f4f6;
    padding: 10px;
    border-radius: 4px;
    font-size: 0.85rem;
}

.metric-small .label {
    font-weight: 600;
    color: var(--text);
    margin-bottom: 4px;
}

.metric-small .value {
    color: var(--primary);
    font-weight: 700;
    font-size: 0.9rem;
}

/* Spread Details */
.spread-details {
    background: #f9fafb;
    padding: 12px;
    border-radius: 4px;
    margin: 12px 0;
}

.spread-details p {
    font-size: 0.85rem;
    margin-bottom: 8px;
    color: var(--text-light);
}

.spread-details p:last-child {
    margin-bottom: 0;
}

/* Featured Card */
.spread-card.featured-card {
    border: 2px solid var(--primary);
    box-shadow: 0 4px 12px rgba(30, 64, 175, 0.1);
}

.spread-link.primary {
    background: var(--primary);
    color: white;
    padding: 10px 14px;
    border-radius: 6px;
    display: inline-block;
    text-decoration: none;
    transition: all 0.2s ease;
}

.spread-link.primary:hover {
    background: var(--primary-light);
    transform: translateX(4px);
}

/* Comparison Section */
.comparison-section {
    background: #f9fafb;
    padding: 20px;
    border-radius: 8px;
    margin-top: 30px;
    border: 1px solid var(--border);
}

.comparison-section h3 {
    margin-top: 0;
}

.spread-comparison-table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 16px;
}

.spread-comparison-table thead {
    background: var(--primary);
    color: white;
}

.spread-comparison-table th {
    padding: 12px;
    text-align: left;
    font-weight: 600;
    font-size: 0.9rem;
}

.spread-comparison-table td {
    padding: 12px;
    border-bottom: 1px solid var(--border);
    font-size: 0.9rem;
}

.spread-comparison-table tbody tr:hover {
    background: #f0f9ff;
}

.strategy-tips h4 {
    margin-top: 0;
}

.strategy-tips ul {
    list-style: none;
    padding: 0;
}

.strategy-tips li {
    padding: 8px 0;
    color: var(--text-light);
}

.strategy-tips li:before {
    content: "✓ ";
    color: var(--success);
    font-weight: 700;
    margin-right: 8px;
}

/* Other Spreads */
.other-spreads {
    background: var(--card-bg);
    padding: 40px 20px;
    border-radius: 12px;
    box-shadow: var(--shadow);
}

.spreads-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 24px;
    margin: 30px 0;
}

.spread-card {
    background: #f9fafb;
    padding: 24px;
    border-radius: 8px;
    border: 2px solid var(--border);
    transition: all 0.3s ease;
}

.spread-card:hover {
    box-shadow: var(--shadow-lg);
    transform: translateY(-4px);
    border-color: var(--primary);
}

.spread-card h3 {
    margin-top: 0;
    margin-bottom: 12px;
}

.spread-card p {
    margin-bottom: 12px;
}

.spread-card ul {
    list-style: none;
    padding: 0;
    margin-bottom: 16px;
}

.spread-card li {
    padding: 4px 0;
    font-size: 0.9rem;
    color: var(--text-light);
}

.spread-card li:before {
    content: "• ";
    color: var(--primary);
    margin-right: 6px;
    font-weight: 700;
}

.spread-link {
    display: inline-block;
    color: var(--primary);
    text-decoration: none;
    font-weight: 600;
    transition: all 0.2s ease;
}

.spread-link:hover {
    color: var(--primary-light);
    text-decoration: underline;
}

/* Guide */
.guide {
    background: var(--card-bg);
    padding: 40px 20px;
    border-radius: 12px;
    box-shadow: var(--shadow);
}

.spread-types-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 20px;
    margin: 20px 0;
}

.type-card {
    background: var(--bg);
    padding: 20px;
    border-radius: 8px;
    border: 1px solid var(--border);
}

.type-card h4 {
    margin-top: 0;
}

.type-card p {
    margin-bottom: 8px;
    font-size: 0.9rem;
}

.type-card p:last-child {
    margin-bottom: 0;
}

/* Strategy Detail */
.strategy-detail {
    background: #f9fafb;
    padding: 20px;
    border-radius: 8px;
    border-left: 4px solid var(--primary);
    margin: 20px 0;
}

.strategy-detail h4 {
    margin-top: 20px;
}

.strategy-detail h4:first-of-type {
    margin-top: 0;
}

.strategy-detail ul {
    list-style: none;
    padding: 0;
}

.strategy-detail li {
    padding: 8px 0;
    color: var(--text-light);
}

/* Mistakes Grid */
.mistakes-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 20px;
    margin: 20px 0;
}

.mistake-card {
    background: #fef2f2;
    padding: 20px;
    border-radius: 8px;
    border-left: 4px solid var(--danger);
}

.mistake-card h4 {
    margin-top: 0;
    color: var(--danger);
}

.mistake-card p {
    margin-bottom: 0;
    font-size: 0.9rem;
}

/* FAQs */
.faqs {
    background: var(--card-bg);
    padding: 40px 20px;
    border-radius: 12px;
    box-shadow: var(--shadow);
}

.faqs h2 {
    margin-bottom: 30px;
}

.faq-item {
    margin-bottom: 24px;
    padding-bottom: 24px;
    border-bottom: 1px solid var(--border);
}

.faq-item:last-child {
    border-bottom: none;
    margin-bottom: 0;
    padding-bottom: 0;
}

.faq-item h3 {
    font-size: 1.05rem;
    margin-top: 0;
    margin-bottom: 12px;
}

.faq-item p {
    margin-bottom: 0;
}

/* Footer */
.footer {
    background: var(--text);
    color: white;
    text-align: center;
    padding: 30px 20px;
    margin-top: 60px;
}

.footer p {
    color: rgba(255, 255, 255, 0.8);
    margin: 0;
}

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

    section h2 {
        font-size: 1.6rem;
    }

    .inputs-grid,
    .results-grid,
    .metrics-grid,
    .spreads-grid,
    .spread-types-grid,
    .mistakes-grid {
        grid-template-columns: 1fr;
    }

    table {
        font-size: 0.8rem;
    }

    th, td {
        padding: 6px 4px;
    }
}