/* ==========================================================================
   Learning AutoML - O'Reilly Book Companion Site
   ========================================================================== */

/* CSS Variables */
:root {
    /* O'Reilly-inspired colors */
    --oreilly-red: #d43d41;
    --oreilly-dark: #1a1a2e;
    --oreilly-navy: #16213e;
    --accent-blue: #0f3460;
    --accent-teal: #00b4d8;

    /* Neutral palette */
    --white: #ffffff;
    --gray-50: #f8f9fa;
    --gray-100: #f1f3f5;
    --gray-200: #e9ecef;
    --gray-300: #dee2e6;
    --gray-400: #ced4da;
    --gray-500: #adb5bd;
    --gray-600: #6c757d;
    --gray-700: #495057;
    --gray-800: #343a40;
    --gray-900: #212529;

    /* Case study colors */
    --fraud-color: #6366f1;
    --retail-color: #10b981;
    --healthcare-color: #f59e0b;

    /* Typography */
    --font-sans: 'Source Sans 3', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-serif: 'Merriweather', Georgia, serif;
    --font-mono: 'Source Code Pro', 'Consolas', monospace;

    /* Spacing */
    --space-xs: 0.25rem;
    --space-sm: 0.5rem;
    --space-md: 1rem;
    --space-lg: 1.5rem;
    --space-xl: 2rem;
    --space-2xl: 3rem;
    --space-3xl: 4rem;

    /* Border radius */
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-xl: 16px;

    /* Shadows */
    --shadow-sm: 0 1px 2px rgba(0,0,0,0.05);
    --shadow-md: 0 4px 6px -1px rgba(0,0,0,0.1), 0 2px 4px -1px rgba(0,0,0,0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0,0,0,0.1), 0 4px 6px -2px rgba(0,0,0,0.05);
    --shadow-xl: 0 20px 25px -5px rgba(0,0,0,0.1), 0 10px 10px -5px rgba(0,0,0,0.04);

    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-base: 250ms ease;
    --transition-slow: 350ms ease;
}

/* Reset & Base */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    scroll-behavior: smooth;
    font-size: 16px;
}

body {
    font-family: var(--font-sans);
    color: var(--gray-800);
    line-height: 1.6;
    background: var(--white);
    -webkit-font-smoothing: antialiased;
}

img {
    max-width: 100%;
    height: auto;
    display: block;
}

a {
    color: inherit;
    text-decoration: none;
}

ul {
    list-style: none;
}

/* Container */
.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--space-lg);
}

/* ==========================================================================
   Navigation
   ========================================================================== */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 1000;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--gray-200);
    transition: var(--transition-base);
}

.navbar .container {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 64px;
}

.logo {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    font-weight: 700;
    font-size: 1.125rem;
    color: var(--oreilly-dark);
}

.logo-icon {
    font-size: 1.5rem;
}

.nav-links {
    display: flex;
    align-items: center;
    gap: var(--space-xl);
}

.nav-links a {
    font-weight: 500;
    color: var(--gray-600);
    transition: color var(--transition-fast);
}

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

.mobile-menu-btn {
    display: none;
    flex-direction: column;
    gap: 5px;
    background: none;
    border: none;
    cursor: pointer;
    padding: var(--space-sm);
}

.mobile-menu-btn span {
    width: 24px;
    height: 2px;
    background: var(--gray-700);
    border-radius: 2px;
    transition: var(--transition-fast);
}

/* ==========================================================================
   Buttons
   ========================================================================== */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 0.625rem 1.25rem;
    font-family: var(--font-sans);
    font-weight: 600;
    font-size: 0.875rem;
    border-radius: var(--radius-md);
    border: 2px solid transparent;
    cursor: pointer;
    transition: all var(--transition-fast);
    text-decoration: none;
}

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

.btn-primary:hover {
    background: #c13136;
    border-color: #c13136;
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

.btn-secondary {
    background: var(--white);
    color: var(--gray-800);
    border-color: var(--gray-300);
}

.btn-secondary:hover {
    border-color: var(--gray-400);
    background: var(--gray-50);
}

.btn-outline {
    background: transparent;
    color: var(--oreilly-red);
    border-color: var(--oreilly-red);
}

.btn-outline:hover {
    background: var(--oreilly-red);
    color: var(--white);
}

.btn-case {
    background: transparent;
    color: var(--white);
    border-color: rgba(255,255,255,0.5);
    width: 100%;
    margin-top: auto;
}

.btn-case:hover {
    background: rgba(255,255,255,0.1);
    border-color: var(--white);
}

/* ==========================================================================
   Hero Section
   ========================================================================== */
.hero {
    position: relative;
    padding: 8rem 0 5rem;
    background: linear-gradient(135deg, var(--oreilly-dark) 0%, var(--oreilly-navy) 50%, var(--accent-blue) 100%);
    color: var(--white);
    overflow: hidden;
}

.hero-bg {
    position: absolute;
    inset: 0;
    background-image:
        radial-gradient(circle at 20% 80%, rgba(212, 61, 65, 0.15) 0%, transparent 40%),
        radial-gradient(circle at 80% 20%, rgba(0, 180, 216, 0.1) 0%, transparent 40%);
    pointer-events: none;
}

.hero .container {
    display: grid;
    grid-template-columns: 1fr 400px;
    gap: var(--space-3xl);
    align-items: center;
    position: relative;
}

.hero-badge {
    display: inline-block;
    padding: 0.375rem 0.875rem;
    background: rgba(255,255,255,0.1);
    border: 1px solid rgba(255,255,255,0.2);
    border-radius: 20px;
    font-size: 0.75rem;
    font-weight: 600;
    letter-spacing: 0.05em;
    text-transform: uppercase;
    margin-bottom: var(--space-md);
}

.hero h1 {
    font-family: var(--font-serif);
    font-size: 3.5rem;
    font-weight: 700;
    line-height: 1.1;
    margin-bottom: var(--space-sm);
}

.hero-subtitle {
    font-size: 1.25rem;
    font-weight: 300;
    color: rgba(255,255,255,0.8);
    margin-bottom: var(--space-lg);
}

.hero-description {
    font-size: 1.0625rem;
    color: rgba(255,255,255,0.7);
    line-height: 1.7;
    margin-bottom: var(--space-xl);
    max-width: 540px;
}

.hero-actions {
    display: flex;
    gap: var(--space-md);
    margin-bottom: var(--space-2xl);
}

.hero-stats {
    display: flex;
    gap: var(--space-2xl);
}

.stat {
    text-align: center;
}

.stat-number {
    display: block;
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--white);
    line-height: 1;
}

.stat-label {
    font-size: 0.875rem;
    color: rgba(255,255,255,0.6);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

/* Book Cover Visual */
.hero-visual {
    display: flex;
    justify-content: center;
    perspective: 1000px;
}

.book-cover-img {
    max-width: 320px;
    height: auto;
    border-radius: 4px;
    box-shadow: 0 20px 40px rgba(0,0,0,0.4);
    transform: rotateY(-8deg);
    animation: float 6s ease-in-out infinite;
}

@keyframes float {
    0%, 100% { transform: rotateY(-8deg) translateY(0); }
    50% { transform: rotateY(-8deg) translateY(-10px); }
}

/* ==========================================================================
   Tech Bar
   ========================================================================== */
.tech-bar {
    background: var(--gray-900);
    padding: var(--space-md) 0;
    overflow: hidden;
}

.tech-items {
    display: flex;
    justify-content: center;
    gap: var(--space-2xl);
    flex-wrap: wrap;
}

.tech-item {
    color: var(--gray-400);
    font-size: 0.875rem;
    font-weight: 500;
    letter-spacing: 0.02em;
}

/* ==========================================================================
   Section Headers
   ========================================================================== */
.section-header {
    text-align: center;
    margin-bottom: var(--space-3xl);
}

.section-header h2 {
    font-family: var(--font-serif);
    font-size: 2.25rem;
    font-weight: 700;
    color: var(--gray-900);
    margin-bottom: var(--space-sm);
}

.section-header p {
    font-size: 1.125rem;
    color: var(--gray-600);
}

/* ==========================================================================
   Chapters Section
   ========================================================================== */
.chapters {
    padding: var(--space-3xl) 0;
    background: var(--gray-50);
}

.chapter-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--space-lg);
}

.chapter-card {
    background: var(--white);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    box-shadow: var(--shadow-sm);
    border: 1px solid var(--gray-200);
    transition: all var(--transition-base);
    display: flex;
    flex-direction: column;
}

.chapter-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
    border-color: var(--gray-300);
}

.chapter-card.featured {
    border-color: var(--oreilly-red);
    border-width: 2px;
}

.chapter-number {
    font-family: var(--font-mono);
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--gray-200);
    line-height: 1;
    margin-bottom: var(--space-md);
}

.chapter-card:hover .chapter-number {
    color: var(--oreilly-red);
}

.chapter-content h3 {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--gray-900);
    margin-bottom: var(--space-sm);
}

.chapter-content p {
    font-size: 0.9375rem;
    color: var(--gray-600);
    line-height: 1.6;
    margin-bottom: var(--space-md);
}

.chapter-topics {
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-xs);
    margin-bottom: var(--space-lg);
}

.chapter-topics li {
    font-size: 0.75rem;
    color: var(--gray-600);
    background: var(--gray-100);
    padding: 0.25rem 0.625rem;
    border-radius: 20px;
}

.chapter-link {
    display: inline-flex;
    align-items: center;
    gap: var(--space-sm);
    font-weight: 600;
    color: var(--oreilly-red);
    margin-top: auto;
    transition: gap var(--transition-fast);
}

.chapter-link:hover {
    gap: var(--space-md);
}

.chapter-link .arrow {
    transition: transform var(--transition-fast);
}

.chapter-link:hover .arrow {
    transform: translateX(4px);
}

/* ==========================================================================
   Case Studies Section
   ========================================================================== */
.case-studies {
    padding: var(--space-3xl) 0;
    background: var(--white);
}

.case-study-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--space-lg);
}

.case-study-card {
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    color: var(--white);
    display: flex;
    flex-direction: column;
    min-height: 400px;
    position: relative;
    overflow: hidden;
}

.case-study-card::before {
    content: '';
    position: absolute;
    inset: 0;
    background: linear-gradient(180deg, transparent 0%, rgba(0,0,0,0.3) 100%);
    pointer-events: none;
}

.case-study-card > * {
    position: relative;
    z-index: 1;
}

.case-study-card.fraud {
    background: linear-gradient(135deg, var(--fraud-color) 0%, #4f46e5 100%);
}

.case-study-card.retail {
    background: linear-gradient(135deg, var(--retail-color) 0%, #059669 100%);
}

.case-study-card.healthcare {
    background: linear-gradient(135deg, var(--healthcare-color) 0%, #d97706 100%);
}

.case-icon {
    font-size: 2.5rem;
    margin-bottom: var(--space-md);
}

.case-badge {
    display: inline-block;
    padding: 0.25rem 0.75rem;
    background: rgba(255,255,255,0.2);
    border-radius: 20px;
    font-size: 0.6875rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: var(--space-md);
    width: fit-content;
}

.case-study-card h3 {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: var(--space-sm);
}

.case-study-card > p {
    font-size: 0.9375rem;
    opacity: 0.9;
    line-height: 1.6;
    margin-bottom: var(--space-lg);
}

.case-metrics {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--space-sm);
    margin-bottom: var(--space-lg);
}

.metric {
    text-align: center;
}

.metric-value {
    display: block;
    font-size: 1.25rem;
    font-weight: 700;
    line-height: 1.2;
}

.metric-label {
    font-size: 0.6875rem;
    opacity: 0.8;
    text-transform: uppercase;
    letter-spacing: 0.03em;
}

/* ==========================================================================
   Getting Started Section
   ========================================================================== */
.getting-started {
    padding: var(--space-3xl) 0;
    background: var(--gray-50);
}

.setup-steps {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: var(--space-lg);
    margin-bottom: var(--space-2xl);
    max-width: 800px;
    margin-left: auto;
    margin-right: auto;
}

.step {
    background: var(--white);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    box-shadow: var(--shadow-sm);
    border: 1px solid var(--gray-200);
    overflow: hidden;
    min-width: 0;
}

.step-number {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 36px;
    height: 36px;
    background: var(--oreilly-red);
    color: var(--white);
    font-weight: 700;
    border-radius: 50%;
    margin-bottom: var(--space-md);
}

.step h3 {
    font-size: 1rem;
    font-weight: 700;
    color: var(--gray-900);
    margin-bottom: var(--space-md);
}

.code-block {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    background: var(--gray-900);
    border-radius: var(--radius-md);
    padding: 0.75rem 1rem;
    overflow: hidden;
    max-width: 100%;
}

.code-block code {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    color: var(--gray-300);
    flex: 1;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.copy-btn {
    background: none;
    border: none;
    cursor: pointer;
    opacity: 0.6;
    transition: opacity var(--transition-fast);
    padding: 0;
}

.copy-btn:hover {
    opacity: 1;
}

.requirements-note {
    background: var(--white);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    border-left: 4px solid var(--oreilly-red);
    max-width: 600px;
    margin: 0 auto;
}

.requirements-note h4 {
    font-size: 1rem;
    color: var(--gray-900);
    margin-bottom: var(--space-md);
}

.requirements-note ul {
    display: grid;
    gap: var(--space-sm);
}

.requirements-note li {
    font-size: 0.9375rem;
    color: var(--gray-600);
    padding-left: var(--space-lg);
    position: relative;
}

.requirements-note li::before {
    content: '✓';
    position: absolute;
    left: 0;
    color: var(--oreilly-red);
    font-weight: 600;
}

/* ==========================================================================
   Footer
   ========================================================================== */
.footer {
    background: var(--gray-900);
    color: var(--gray-400);
    padding: var(--space-3xl) 0 var(--space-xl);
}

.footer-content {
    display: grid;
    grid-template-columns: 2fr 1fr 1fr;
    gap: var(--space-3xl);
    margin-bottom: var(--space-2xl);
}

.footer-brand .logo-icon {
    font-size: 2rem;
}

.footer-brand .logo-text {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--white);
}

.footer-brand p {
    margin-top: var(--space-sm);
    font-size: 0.875rem;
}

.footer-links h4 {
    color: var(--white);
    font-size: 0.875rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: var(--space-md);
}

.footer-links ul {
    display: grid;
    gap: var(--space-sm);
}

.footer-links a {
    font-size: 0.9375rem;
    transition: color var(--transition-fast);
}

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

.footer-bottom {
    padding-top: var(--space-xl);
    border-top: 1px solid var(--gray-800);
    text-align: center;
    font-size: 0.875rem;
}

/* ==========================================================================
   Responsive Design
   ========================================================================== */
@media (max-width: 1024px) {
    .hero .container {
        grid-template-columns: 1fr;
        text-align: center;
    }

    .hero-description {
        max-width: none;
    }

    .hero-actions {
        justify-content: center;
    }

    .hero-stats {
        justify-content: center;
    }

    .hero-visual {
        display: none;
    }

    .chapter-grid {
        grid-template-columns: repeat(2, 1fr);
    }

    .case-study-grid {
        grid-template-columns: repeat(2, 1fr);
    }

    .case-study-grid .case-study-card:last-child {
        grid-column: span 2;
    }

    .footer-content {
        grid-template-columns: 1fr 1fr;
    }
}

@media (max-width: 768px) {
    .nav-links {
        display: none;
    }

    .mobile-menu-btn {
        display: flex;
    }

    .hero {
        padding: 6rem 0 3rem;
    }

    .hero h1 {
        font-size: 2.5rem;
    }

    .hero-subtitle {
        font-size: 1.125rem;
    }

    .hero-stats {
        flex-direction: column;
        gap: var(--space-lg);
    }

    .chapter-grid,
    .case-study-grid {
        grid-template-columns: 1fr;
    }

    .case-study-grid .case-study-card:last-child {
        grid-column: span 1;
    }

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

    .footer-content {
        grid-template-columns: 1fr;
        text-align: center;
    }

    .section-header h2 {
        font-size: 1.75rem;
    }
}

@media (max-width: 480px) {
    .hero h1 {
        font-size: 2rem;
    }

    .hero-actions {
        flex-direction: column;
    }

    .btn {
        width: 100%;
    }

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