:root {
    --text-main: #111827;
    --text-muted: #6b7280;
    --bg-main: #ffffff;
    --bg-muted: #f9fafb;
    --border-color: #e5e7eb;
    --accent: #0f172a;
    --accent-hover: #374151;
    --link-color: #2563eb;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    margin: 0;
    padding: 0;
    color: var(--text-main);
    background-color: var(--bg-main);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

/* Navigation */
nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 20px 40px;
    border-bottom: 1px solid var(--border-color);
}
.nav-logo {
    font-size: 1.25rem;
    font-weight: 800;
    text-decoration: none;
    color: var(--text-main);
    letter-spacing: -0.02em;
    text-transform: uppercase;
}
.nav-links a {
    margin-left: 24px;
    text-decoration: none;
    color: var(--text-muted);
    font-size: 0.95rem;
    font-weight: 500;
    transition: color 0.2s;
}
.nav-links a:hover {
    color: var(--text-main);
}

/* Layout Containers */
.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 40px 20px 80px 20px;
}
.article-container {
    max-width: 760px;
    margin: 0 auto;
    padding: 40px 20px;
}

/* Split Hero Section */
.hero {
    text-align: center;
    padding: 0 0 80px 0;
}
.split-hero {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 60px;
    text-align: left;
}
.split-hero .hero-content {
    flex: 1.2;
}
.split-hero .hero-visual {
    flex: 0.8;
    display: flex;
    justify-content: center;
}

h1 {
    font-size: 3.5rem;
    font-weight: 800;
    letter-spacing: -0.04em;
    margin: 0 0 20px 0;
    line-height: 1.1;
}
.hero-subtitle {
    font-size: 1.25rem;
    color: var(--text-muted);
    margin: 0 0 40px 0;
    line-height: 1.6;
}

/* Book Cover Placeholder */
.book-cover-placeholder {
    width: 100%;
    max-width: 320px;
    aspect-ratio: 2 / 3;
    background: #f1f5f9;
    border: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    color: #94a3b8;
    font-weight: 600;
    font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
    border-radius: 4px;
    box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.25);
}

.shop-links p {
    margin-bottom: 12px;
    color: var(--text-main);
}

/* Section Divider */
.section-divider {
    text-align: center;
    margin: 60px 0 20px 0;
}
.section-divider h2 {
    font-size: 2rem;
    letter-spacing: -0.02em;
}

/* Typography for Summary */
.summary-section h2 {
    margin-top: 0;
    font-size: 2.2rem;
    letter-spacing: -0.03em;
    border-bottom: 2px solid var(--border-color);
    padding-bottom: 16px;
    margin-bottom: 24px;
}
.summary-section .lead {
    font-size: 1.25rem;
    color: var(--accent);
    font-weight: 500;
}
.summary-section p {
    font-size: 1.1rem;
    color: #374151;
    margin-bottom: 24px;
}

/* Grid & Cards */
.grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: 24px;
}
.card {
    display: block;
    background: var(--bg-main);
    border: 1px solid var(--border-color);
    padding: 32px;
    border-radius: 8px;
    transition: all 0.2s ease-in-out;
}
.card:hover {
    border-color: var(--text-muted);
    transform: translateY(-2px);
    box-shadow: 0 12px 20px -8px rgba(0, 0, 0, 0.08);
}
.card h3 {
    margin: 0 0 16px 0;
    font-size: 1.25rem;
    letter-spacing: -0.01em;
}
.card p {
    margin: 0;
    color: var(--text-muted);
    font-size: 0.95rem;
}

/* Buttons */
.btn {
    display: inline-block;
    background-color: var(--accent);
    color: white;
    padding: 12px 28px;
    text-decoration: none;
    border-radius: 6px;
    font-weight: 600;
    transition: background-color 0.2s;
}
.btn:hover {
    background-color: var(--accent-hover);
}
.btn-outline {
    background-color: transparent;
    color: var(--accent);
    border: 1px solid var(--border-color);
    margin-left: 12px;
}
.btn-outline:hover {
    background-color: var(--bg-muted);
}

/* Footer */
footer {
    text-align: center;
    padding: 40px 20px;
    border-top: 1px solid var(--border-color);
    color: var(--text-muted);
    font-size: 0.9rem;
    margin-top: 80px;
}

@media (max-width: 850px) {
    h1 { font-size: 2.8rem; }
    .split-hero {
        flex-direction: column-reverse;
        text-align: center;
        gap: 40px;
    }
    .btn-outline {
        margin-left: 0;
        margin-top: 12px;
        display: block;
    }
}