@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&display=swap');

:root {
    --bg-color: #ffffff;
    --text-color: #1a1a1a;
    --text-muted: #666666;
    --accent-color: #000000;
    --secondary-color: #f7f7f7;
    --border-color: #e5e5e5;
    --card-bg: #ffffff;
    --max-width: 1100px;
    --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    --radius: 12px;
    --transition: all 0.3s ease;
}

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

body {
    font-family: var(--font-sans);
    line-height: 1.6;
    color: var(--text-color);
    background-color: var(--bg-color);
    -webkit-font-smoothing: antialiased;
    overflow-x: hidden;
}

/* Typography */
h1, h2, h3, h4 {
    font-weight: 700;
    line-height: 1.1;
    margin-bottom: 1.5rem;
    letter-spacing: -0.02em;
}

h1 { font-size: 4rem; }
h2 { font-size: 2.5rem; }
h3 { font-size: 1.75rem; }

p {
    margin-bottom: 1.5rem;
    color: var(--text-muted);
    font-size: 1.1rem;
}

.eyebrow {
    display: block;
    font-size: 0.875rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--text-muted);
    margin-bottom: 1rem;
}

/* Layout */
.container {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 0 2rem;
}

section {
    padding: 8rem 0;
}

.section-header {
    max-width: 700px;
    margin-bottom: 4rem;
}

/* Navigation */
nav {
    position: fixed;
    top: 0;
    width: 100%;
    z-index: 100;
    background: rgba(255, 255, 255, 0.8);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--border-color);
    padding: 1rem 0;
}

nav .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    font-weight: 700;
    font-size: 1.25rem;
    text-decoration: none;
    color: var(--accent-color);
}

.nav-links {
    display: flex;
    gap: 2rem;
    list-style: none;
}

.nav-links a {
    text-decoration: none;
    color: var(--text-muted);
    font-size: 0.9rem;
    font-weight: 500;
    transition: var(--transition);
}

.nav-links a:hover {
    color: var(--accent-color);
}

.nav-secondary {
    opacity: 0.6;
}

/* Components */
.btn {
    display: inline-block;
    padding: 0.8rem 1.5rem;
    border-radius: var(--radius);
    text-decoration: none;
    font-weight: 500;
    transition: var(--transition);
    cursor: pointer;
}

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

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 10px 20px rgba(0,0,0,0.1);
}

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

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

.card {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    padding: 2.5rem;
    border-radius: var(--radius);
    transition: var(--transition);
}

.card:hover {
    box-shadow: 0 20px 40px rgba(0,0,0,0.03);
}

.definition-block {
    background: var(--secondary-color);
    padding: 3rem;
    border-radius: var(--radius);
    border-left: 4px solid var(--accent-color);
    margin: 3rem 0;
}

.definition-block p {
    font-size: 1.5rem;
    color: var(--text-color);
    font-weight: 400;
    margin-bottom: 0;
}

.formula-block {
    text-align: center;
    padding: 4rem 0;
    font-size: 2rem;
    font-weight: 600;
}

.formula-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 2rem;
    margin-top: 3rem;
}

.comparison-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 4rem;
    margin-top: 4rem;
}

.comparison-col h3 {
    padding-bottom: 1rem;
    border-bottom: 2px solid var(--accent-color);
    margin-bottom: 2rem;
}

.comparison-list {
    list-style: none;
}

.comparison-list li {
    padding: 0.75rem 0;
    border-bottom: 1px solid var(--border-color);
    color: var(--text-muted);
}

.comparison-list li::before {
    content: "—";
    margin-right: 0.5rem;
}

/* Tables */
table {
    width: 100%;
    border-collapse: collapse;
    margin: 2rem 0;
}

th, td {
    text-align: left;
    padding: 1.25rem;
    border-bottom: 1px solid var(--border-color);
}

th {
    font-weight: 600;
    color: var(--accent-color);
    background: var(--secondary-color);
}

/* FAQ */
.faq-item {
    border-bottom: 1px solid var(--border-color);
    padding: 1.5rem 0;
}

.faq-question {
    font-weight: 600;
    font-size: 1.2rem;
    margin-bottom: 1rem;
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.faq-answer {
    color: var(--text-muted);
}

/* Footer */
footer {
    background: var(--secondary-color);
    padding: 6rem 0;
    border-top: 1px solid var(--border-color);
}

.footer-grid {
    display: grid;
    grid-template-columns: 2fr 1fr 1fr;
    gap: 4rem;
}

.footer-links {
    list-style: none;
}

.footer-links li {
    margin-bottom: 0.8rem;
}

.footer-links a {
    text-decoration: none;
    color: var(--text-muted);
    font-size: 0.9rem;
    transition: var(--transition);
}

.footer-links a:hover {
    color: var(--accent-color);
}

/* Utilities */
.text-center { text-align: center; }
.mt-4 { margin-top: 2rem; }
.mb-4 { margin-bottom: 2rem; }
.divider { height: 1px; background: var(--border-color); margin: 4rem 0; }

@media (max-width: 768px) {
    h1 { font-size: 2.5rem; }
    h2 { font-size: 1.75rem; }
    .nav-links { display: none; }
    .comparison-grid, .formula-grid, .footer-grid {
        grid-template-columns: 1fr;
    }
    section { padding: 4rem 0; }
}

/* Stack Diagram */
.stack-container {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
    margin: 4rem 0;
}

.stack-layer {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    padding: 1.5rem;
    border-radius: var(--radius);
    text-align: center;
    font-weight: 600;
    transition: var(--transition);
}

.stack-layer:hover {
    background: var(--secondary-color);
    transform: scale(1.02);
}

/* Loop Diagram */
.loop-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 1.5rem;
    margin: 4rem 0;
}

.loop-card {
    text-align: center;
    padding: 2rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    background: var(--card-bg);
}

.loop-card h4 {
    margin-bottom: 0.5rem;
    color: var(--accent-color);
}