:root {
    --bg-main: #f8fafc;
    --bg-card: rgba(255, 255, 255, 0.85);
    --bg-card-hover: rgba(255, 255, 255, 1);
    --border-color: rgba(15, 23, 42, 0.08);
    --border-hover: rgba(37, 99, 235, 0.4);
    --text-primary: #0f172a;
    --text-secondary: #475569;
    --text-muted: #94a3b8;
    --primary: #2563eb;
    --primary-glow: rgba(37, 99, 235, 0.08);
    --secondary: #0891b2;
    --accent: #10b981;
    --orange: #f97316;
    --orange-hover: #ea580c;
    --orange-glow: rgba(249, 115, 22, 0.15);
    --transition-fast: 0.2s ease;
    --transition-normal: 0.3s ease;
    --font-sans: 'Inter', sans-serif;
    --font-heading: 'Outfit', sans-serif;
    --max-width: 1200px;
}

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

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

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

/* Custom Scrollbar */
::-webkit-scrollbar {
    width: 8px;
}

::-webkit-scrollbar-track {
    background: var(--bg-main);
}

::-webkit-scrollbar-thumb {
    background: rgba(0, 0, 0, 0.1);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--text-muted);
}

/* Typography */
h1,
h2,
h3,
h4 {
    font-family: var(--font-heading);
    font-weight: 700;
    letter-spacing: -0.02em;
}

a {
    color: inherit;
    text-decoration: none;
    transition: color var(--transition-fast);
}

/* Header & Navigation */
header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 100;
    background: rgba(248, 250, 252, 0.8);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--border-color);
}

.nav-container {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 1.25rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    font-family: var(--font-heading);
    font-size: 1.25rem;
    font-weight: 800;
    background: linear-gradient(135deg, var(--text-primary) 30%, var(--primary) 100%);
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.logo span {
    color: var(--secondary);
    -webkit-text-fill-color: initial;
}

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

.nav-links a {
    font-size: 0.9rem;
    font-weight: 500;
    color: var(--text-secondary);
}

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

.nav-links a:focus-visible,
.nav-menu-toggle:focus-visible {
    outline: 3px solid var(--primary);
    outline-offset: 3px;
}

.nav-links a.active {
    color: var(--text-primary);
    font-weight: 700;
}

.nav-links a.btn {
    color: white;
}

.nav-links a.btn:hover {
    color: white;
}

.nav-links a.language-switch {
    min-width: 4.6rem;
    padding: 0.38rem 0.7rem;
    border: 1px solid var(--border-color);
    border-radius: 999px;
    background: var(--bg-card);
    color: var(--text-primary);
    font-size: 0.78rem;
    font-weight: 700;
    letter-spacing: 0.01em;
    text-align: center;
}

.nav-links a.language-switch:hover {
    border-color: var(--primary);
    color: var(--primary);
}

.nav-menu-toggle {
    display: none;
    align-items: center;
    gap: 0.6rem;
    min-height: 44px;
    padding: 0.65rem 0.85rem;
    color: var(--text-primary);
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 10px;
    font: 600 0.9rem var(--font-body);
    cursor: pointer;
}

.nav-menu-icon,
.nav-menu-icon::before,
.nav-menu-icon::after {
    display: block;
    width: 18px;
    height: 2px;
    background: currentColor;
    border-radius: 2px;
    transition: transform var(--transition-fast), opacity var(--transition-fast);
}

.nav-menu-icon {
    position: relative;
}

.nav-menu-icon::before,
.nav-menu-icon::after {
    position: absolute;
    left: 0;
    content: "";
}

.nav-menu-icon::before {
    top: -6px;
}

.nav-menu-icon::after {
    top: 6px;
}

.nav-menu-toggle[aria-expanded="true"] .nav-menu-icon {
    background: transparent;
}

.nav-menu-toggle[aria-expanded="true"] .nav-menu-icon::before {
    top: 0;
    transform: rotate(45deg);
}

.nav-menu-toggle[aria-expanded="true"] .nav-menu-icon::after {
    top: 0;
    transform: rotate(-45deg);
}

@media (max-width: 1050px) {
    .nav-menu-toggle {
        display: inline-flex;
        margin-left: auto;
    }

    .nav-links {
        position: absolute;
        top: 100%;
        right: 1rem;
        display: none;
        width: min(320px, calc(100vw - 2rem));
        padding: 0.75rem;
        gap: 0.35rem;
        flex-direction: column;
        align-items: stretch;
        background: rgba(248, 250, 252, 0.98);
        border: 1px solid var(--border-color);
        border-radius: 12px;
        box-shadow: var(--shadow-lg);
    }

    .nav-links.is-open {
        display: flex;
    }

    .nav-links a {
        display: block;
        padding: 0.7rem 0.8rem;
        font-size: 0.85rem;
    }

    .nav-links a.btn {
        padding: 0.55rem 0.8rem;
        font-size: 0.82rem;
    }

    .nav-links a.language-switch {
        min-width: 0;
        padding: 0.7rem 0.8rem;
        font-size: 0.85rem;
        text-align: left;
    }
}

/* Hero Section */
.hero {
    position: relative;
    padding: 9rem 2rem 5rem;
    max-width: var(--max-width);
    margin: 0 auto;
    display: grid;
    grid-template-columns: 1.2fr 0.8fr;
    gap: 4rem;
    align-items: center;
}

.hero-glow {
    position: absolute;
    width: 400px;
    height: 400px;
    background: radial-gradient(circle, var(--primary-glow) 0%, transparent 70%);
    top: 15%;
    right: 5%;
    pointer-events: none;
    z-index: -1;
}

.hero-content h1 {
    font-size: 3.5rem;
    line-height: 1.1;
    margin-bottom: 1.5rem;
    background: linear-gradient(135deg, var(--text-primary) 40%, #1e3a8a 100%);
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}

.hero-content p {
    font-size: 1.15rem;
    color: var(--text-secondary);
    margin-bottom: 2.5rem;
    max-width: 540px;
}

.hero-btns {
    display: flex;
    gap: 1rem;
    flex-wrap: wrap;
}

.hero-proof {
    display: grid;
    gap: 0.7rem;
    list-style: none;
    margin: 0 0 2.3rem;
    max-width: 620px;
}

.hero-proof li {
    position: relative;
    padding-left: 1.2rem;
    color: var(--text-primary);
    font-weight: 500;
    line-height: 1.45;
    overflow-wrap: break-word;
}

.hero-proof li::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0.62em;
    width: 0.45rem;
    height: 0.45rem;
    border-radius: 50%;
    background: var(--secondary);
}

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 0.75rem 1.5rem;
    border-radius: 8px;
    font-weight: 600;
    font-size: 0.95rem;
    transition: all var(--transition-fast);
    cursor: pointer;
}

.btn-primary {
    background: var(--primary);
    color: white;
    border: none;
}

.btn-primary:hover {
    background: #1d4ed8;
    box-shadow: 0 0 20px rgba(37, 99, 235, 0.2);
}

.btn-orange {
    background: var(--orange);
    color: white;
    border: none;
}

.btn-orange:hover {
    background: var(--orange-hover);
    box-shadow: 0 0 20px var(--orange-glow);
}

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

.btn-secondary:hover {
    background: rgba(15, 23, 42, 0.04);
    border-color: var(--text-muted);
}

/* Book Cover Presentation */
.hero-book-wrap {
    perspective: 1000px;
    display: flex;
    justify-content: center;
}

.book-card {
    width: 280px;
    height: 400px;
    background: linear-gradient(145deg, #1e293b, #0f172a);
    border-radius: 12px;
    box-shadow: 0 25px 50px -12px rgba(15, 23, 42, 0.2);
    border: 1px solid rgba(255, 255, 255, 0.1);
    transform: rotateY(-15deg) rotateX(10deg);
    transition: transform var(--transition-normal), box-shadow var(--transition-normal);
    position: relative;
    overflow: hidden;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    padding: 2.5rem 2rem;
}

.book-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 15px;
    height: 100%;
    background: linear-gradient(to right, rgba(0, 0, 0, 0.3) 0%, rgba(255, 255, 255, 0.05) 50%, rgba(0, 0, 0, 0.2) 100%);
    border-right: 1px solid rgba(255, 255, 255, 0.1);
}

.book-card:hover {
    transform: rotateY(-5deg) rotateX(5deg) scale(1.02);
    box-shadow: 0 35px 60px -10px rgba(37, 99, 235, 0.2);
}

.book-card .author {
    font-size: 0.85rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--secondary);
    font-weight: 600;
}

.book-card .title {
    font-family: var(--font-heading);
    font-size: 2.2rem;
    line-height: 1.1;
    color: white;
    margin-top: 1rem;
    font-weight: 800;
}

.book-card .subtitle {
    font-size: 0.95rem;
    color: #94a3b8;
    margin-top: 0.5rem;
}

.book-card .badge {
    align-self: flex-start;
    padding: 0.25rem 0.75rem;
    background: rgba(37, 99, 235, 0.2);
    border: 1px solid var(--primary);
    color: #60a5fa;
    font-size: 0.75rem;
    border-radius: 99px;
    font-weight: 600;
}

/* Stats Section */
.stats {
    max-width: var(--max-width);
    margin: 3.5rem auto;
    padding: 0 2rem;
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: 1.25rem;
}

@media (max-width: 992px) {
    .stats {
        grid-template-columns: repeat(3, 1fr);
    }
}

@media (max-width: 640px) {
    .stats {
        grid-template-columns: repeat(2, 1fr);
    }
}

.stat-item {
    background: var(--bg-card);
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
    border: 1px solid var(--border-color);
    padding: 1.5rem 1.25rem;
    border-radius: 14px;
    text-align: center;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.02);
    transition: all var(--transition-fast);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
}

.stat-item:hover {
    border-color: var(--primary);
    transform: translateY(-4px);
    box-shadow: 0 12px 24px rgba(37, 99, 235, 0.08);
}

.stat-icon {
    color: var(--primary);
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 0.75rem;
}

.stat-number {
    font-family: var(--font-heading);
    font-size: 2.2rem;
    font-weight: 800;
    color: var(--text-primary);
    line-height: 1.1;
    margin-bottom: 0.25rem;
}

.stat-label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    font-weight: 600;
    line-height: 1.35;
}

/* Section Header */
.section-header {
    text-align: center;
    max-width: 600px;
    margin: 6rem auto 3rem;
    padding: 0 2rem;
}

.section-header h2 {
    font-size: 2.25rem;
    margin-bottom: 1rem;
    background: linear-gradient(135deg, var(--text-primary) 50%, var(--text-muted) 100%);
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}

.section-header p {
    color: var(--text-secondary);
}

/* TOC Conceptual Model Interactive Component */
.toc-intro-container {
    max-width: 1000px;
    margin: -1.5rem auto 2.5rem;
    padding: 0 2rem;
    width: 100%;
    box-sizing: border-box;
}

.toc-intro-card {
    background: transparent;
    border: none;
    border-radius: 0;
    padding: 0;
    box-shadow: none;
    backdrop-filter: none;
}

.toc-intro-card:hover {
    border-color: transparent;
    box-shadow: none;
}

.toc-intro-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 1rem;
    flex-wrap: wrap;
    gap: 0.75rem;
}

.badge-interactive {
    background: rgba(37, 99, 235, 0.15);
    color: #60a5fa;
    border: 1px solid rgba(37, 99, 235, 0.4);
    padding: 0.35rem 0.85rem;
    border-radius: 99px;
    font-size: 0.78rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.toc-intro-hint {
    font-size: 0.88rem;
    color: var(--text-secondary);
    margin: 0;
    font-weight: 500;
}

.aaa-diagram-wrapper {
    width: 100%;
    position: relative;
    overflow: hidden;
}

.aaa-interactive-svg {
    width: 100%;
    height: auto;
    display: block;
    font-family: 'Outfit', 'Inter', system-ui, sans-serif;
    user-select: none;
}

/* Center Ring animation */
.aaa-ring-img {
    transform-origin: 1200px 715px;
    transition: transform 0.8s cubic-bezier(0.16, 1, 0.3, 1);
}

.toc-intro-card:hover .aaa-ring-img {
    transform: rotate(6deg) scale(1.02);
}

/* Flow line dash animation */
@keyframes flowDash {
    to {
        stroke-dashoffset: -48;
    }
}

.aaa-flow-line {
    animation: flowDash 2.8s linear infinite;
}

/* Node Elements */
.aaa-node {
    cursor: pointer;
    outline: none;
}

.node-bg {
    transition: fill var(--transition-fast), stroke var(--transition-fast), stroke-width var(--transition-fast), filter var(--transition-fast);
}

.bg-orange {
    fill: #0f172a;
    stroke: #f97316;
    stroke-width: 3.5;
}

.bg-blue {
    fill: #0f172a;
    stroke: #38bdf8;
    stroke-width: 3.5;
}

.bg-purple {
    fill: #0f172a;
    stroke: #c084fc;
    stroke-width: 3.5;
}

.center-badge-bg {
    fill: #0f172a;
    stroke: #60a5fa;
    stroke-width: 4;
    transition: fill var(--transition-fast), stroke var(--transition-fast), stroke-width var(--transition-fast), filter var(--transition-fast);
}

/* SVG Text Styles - Crisp & High Contrast */
.txt-node-part {
    font-size: 32px;
    font-weight: 800;
    letter-spacing: 3px;
}
.tag-orange { fill: #f97316; }
.tag-blue { fill: #38bdf8; }
.tag-purple { fill: #c084fc; }
.part-center { fill: #60a5fa; }

.txt-node-title {
    font-size: 58px;
    font-weight: 800;
    fill: #ffffff;
}

.txt-node-desc {
    font-size: 34px;
    font-weight: 600;
    fill: #f1f5f9;
}

.txt-node-sub {
    font-size: 32px;
    font-weight: 500;
    fill: #94a3b8;
}

.txt-node-action {
    font-size: 30px;
    font-weight: 700;
    fill: #60a5fa;
    opacity: 0.9;
    transition: opacity var(--transition-fast);
}

.txt-center-main {
    font-size: 56px;
    font-weight: 800;
    fill: #ffffff;
}

.txt-center-sub {
    font-size: 50px;
    font-weight: 800;
    fill: #93c5fd;
}

.txt-rel-title {
    font-size: 34px;
    font-weight: 800;
}
.rel-orange { fill: #fb923c; }
.rel-blue { fill: #38bdf8; }
.rel-purple { fill: #c084fc; }

.txt-rel-body {
    font-size: 32px;
    fill: #ffffff;
    font-weight: 600;
}

.txt-rel-body-wrapped {
    font-size: 28px;
}

/* Node Hover & Focus States */
.aaa-node:hover .bg-orange,
.aaa-node:focus-visible .bg-orange {
    fill: rgba(249, 115, 22, 0.25);
    stroke: #fb923c;
    stroke-width: 5;
    filter: url(#glow-orange);
}

.aaa-node:hover .bg-blue,
.aaa-node:focus-visible .bg-blue {
    fill: rgba(56, 189, 248, 0.25);
    stroke: #7dd3fc;
    stroke-width: 5;
    filter: url(#glow-blue);
}

.aaa-node:hover .bg-purple,
.aaa-node:focus-visible .bg-purple {
    fill: rgba(192, 132, 252, 0.25);
    stroke: #e9d5ff;
    stroke-width: 5;
    filter: url(#glow-purple);
}

.node-center:hover .center-badge-bg,
.node-center:focus-visible .center-badge-bg {
    fill: rgba(37, 99, 235, 0.35);
    stroke: #93c5fd;
    stroke-width: 5;
    filter: url(#glow-blue);
}

/* TOC Part Filter Navigation Bar */
.toc-filter-bar {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.6rem;
    margin: 0 auto 2.5rem;
    flex-wrap: wrap;
    scroll-margin-top: 5rem;
}

.filter-label {
    font-size: 0.9rem;
    color: var(--text-muted);
    font-weight: 600;
    margin-right: 0.25rem;
}

.toc-filter-btn {
    background: rgba(30, 41, 59, 0.5);
    border: 1px solid var(--border-color);
    color: var(--text-secondary);
    padding: 0.5rem 1.1rem;
    border-radius: 99px;
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.toc-filter-btn:hover {
    color: var(--text-primary);
    border-color: rgba(96, 165, 250, 0.4);
    background: rgba(30, 41, 59, 0.85);
}

.toc-filter-btn.active {
    background: var(--primary);
    color: white;
    border-color: var(--primary);
    box-shadow: 0 0 18px rgba(37, 99, 235, 0.35);
}

/* Detail Panel Chapter Navigation */
.detail-header-nav {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 1.25rem;
    padding-bottom: 0.85rem;
    border-bottom: 1px solid var(--border-color);
    flex-wrap: wrap;
    gap: 0.75rem;
}

.chapter-nav-buttons {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.btn-icon-nav {
    background: rgba(30, 41, 59, 0.6);
    border: 1px solid var(--border-color);
    color: var(--text-primary);
    width: 36px;
    height: 36px;
    border-radius: 8px;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.btn-icon-nav:hover {
    background: var(--primary);
    color: white;
    border-color: var(--primary);
    box-shadow: 0 4px 14px rgba(37, 99, 235, 0.35);
}
/* Interactive Book Content Section */
.toc-section {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 0 2rem;
}

/* Layout for TOC & Details Panel */
.toc-layout {
    display: grid;
    grid-template-columns: 1.1fr 0.9fr;
    gap: 3rem;
    align-items: start;
    margin-bottom: 6rem;
}

.parts-container {
    display: flex;
    flex-direction: column;
    gap: 2.5rem;
}

.part-card {
    background: var(--bg-card);
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
    border: 1px solid var(--border-color);
    border-radius: 16px;
    padding: 2rem;
    box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.02);
}

.part-title {
    font-size: 1.1rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--secondary);
    margin-bottom: 1.5rem;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 0.75rem;
}

.chapters-list {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.chapter-item {
    width: 100%;
    text-align: left;
    font-family: inherit;
    background: rgba(15, 23, 42, 0.02);
    border: 1px solid var(--border-color);
    padding: 1rem 1.25rem;
    border-radius: 8px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: space-between;
    transition: all var(--transition-fast);
}

.chapter-item:hover,
.chapter-item.active {
    background: rgba(37, 99, 235, 0.05);
    border-color: var(--primary);
    transform: translateX(4px);
}

.chapter-item:focus-visible {
    outline: 2px solid var(--primary);
    outline-offset: 2px;
}

.chapter-info {
    display: flex;
    align-items: center;
    gap: 1rem;
}

.chapter-num {
    font-family: var(--font-heading);
    font-weight: 700;
    font-size: 1rem;
    color: var(--text-muted);
    min-width: 25px;
}

.chapter-item:hover .chapter-num,
.chapter-item.active .chapter-num {
    color: var(--secondary);
}

.chapter-title {
    font-weight: 600;
    font-size: 0.95rem;
    color: var(--text-primary);
}

.chapter-chevron {
    color: var(--text-muted);
    font-size: 0.8rem;
    transition: transform var(--transition-fast);
}

.chapter-item:hover .chapter-chevron,
.chapter-item.active .chapter-chevron {
    color: var(--primary);
    transform: translateX(2px);
}

/* Detail Panel Styling */
.details-panel {
    background: var(--bg-card);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border: 1px solid var(--border-color);
    border-radius: 16px;
    padding: 2.5rem;
    position: sticky;
    top: 7rem;
    min-height: 450px;
    box-shadow: 0 10px 15px -3px rgba(0, 0, 0, 0.04);
}

.panel-placeholder {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    height: 350px;
    text-align: center;
    color: var(--text-muted);
    gap: 1rem;
}

.panel-placeholder svg {
    color: var(--border-color);
}

.detail-num {
    font-size: 0.85rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--secondary);
    font-weight: 700;
    margin-bottom: 0.5rem;
}

.detail-title {
    font-size: 1.75rem;
    line-height: 1.2;
    margin-bottom: 1.5rem;
}

.detail-desc {
    color: var(--text-secondary);
    margin-bottom: 2rem;
    font-size: 0.95rem;
}

.detail-section-title {
    font-size: 0.85rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-muted);
    margin-bottom: 0.75rem;
    font-weight: 700;
}

.objectives-list {
    list-style: none;
    margin-bottom: 2rem;
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.objectives-list li {
    font-size: 0.9rem;
    padding-left: 1.5rem;
    position: relative;
    color: var(--text-secondary);
}

.objectives-list li::before {
    content: "→";
    position: absolute;
    left: 0;
    color: var(--primary);
}

.case-study-box {
    background: rgba(37, 99, 235, 0.04);
    border: 1px dashed rgba(37, 99, 235, 0.3);
    border-radius: 8px;
    padding: 1.25rem;
}

.case-study-title {
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 0.5rem;
}

.case-study-desc {
    font-size: 0.85rem;
    color: var(--text-secondary);
}

/* Resources Section */
.resources-grid {
    max-width: var(--max-width);
    margin: 0 auto 6rem;
    padding: 0 2rem;
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 2rem;
}

.resource-card {
    background: var(--bg-card);
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
    border: 1px solid var(--border-color);
    padding: 2.25rem 2rem;
    border-radius: 16px;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.02);
    transition: all var(--transition-fast);
}

.resource-card:hover {
    border-color: var(--border-hover);
    transform: translateY(-5px);
}

.resource-icon {
    color: var(--primary);
}

.resource-card h3 {
    font-size: 1.25rem;
    margin-bottom: 0.75rem;
}

.resource-card p {
    color: var(--text-secondary);
    font-size: 0.9rem;
    margin-bottom: 1.5rem;
}

.resource-link {
    align-self: flex-start;
    color: var(--primary);
    font-weight: 600;
    font-size: 0.9rem;
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
}

.resource-link:hover {
    color: var(--secondary);
}

/* Badge specific style */
.badge {
    display: inline-block;
    padding: 0.25rem 0.75rem;
    background: rgba(37, 99, 235, 0.08);
    border: 1px solid var(--primary);
    color: var(--primary);
    font-size: 0.75rem;
    border-radius: 99px;
    font-weight: 600;
}

/* Author Section */
.author-section {
    max-width: var(--max-width);
    margin: 0 auto 6rem;
    padding: 0 2rem;
}

.author-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 16px;
    padding: 3rem;
    box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.02);
    display: grid;
    grid-template-columns: 0.6fr 1.4fr;
    gap: 3rem;
    align-items: center;
}

.author-image-wrap {
    display: flex;
    justify-content: center;
}

.author-avatar {
    width: 180px;
    height: 180px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--primary), var(--secondary));
    padding: 4px;
    box-shadow: 0 10px 25px rgba(37, 99, 235, 0.1);
}

.author-avatar-img {
    width: 100%;
    height: 100%;
    border-radius: 50%;
    background: #1e293b;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 3rem;
    color: white;
    font-family: var(--font-heading);
    font-weight: 700;
}

.author-info h3 {
    font-size: 1.75rem;
    margin-bottom: 0.5rem;
}

.author-role {
    color: var(--secondary);
    font-weight: 600;
    font-size: 0.95rem;
    margin-bottom: 1.25rem;
}

.author-bio {
    color: var(--text-secondary);
    font-size: 0.95rem;
    margin-bottom: 1.5rem;
}

.author-info .hero-proof li {
    color: var(--text-secondary);
    font-size: 0.95rem;
    font-weight: 400;
}

/* Contact / Newsletter Section */
.contact-section {
    max-width: 600px;
    margin: 0 auto 8rem;
    padding: 0 2rem;
    text-align: center;
}

/* Resource Card Header (Flex for icon next to title) */
.resource-header {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    margin-bottom: 1.25rem;
}

.resource-header h3 {
    margin-bottom: 0;
}

.resource-icon {
    color: var(--primary);
    display: flex;
    align-items: center;
}

.resource-item-link {
    color: var(--primary);
    font-weight: 500;
    text-decoration: none;
    border-bottom: 1px dashed var(--primary);
    transition: all var(--transition-fast);
}

.resource-item-link:hover {
    color: var(--secondary);
    border-color: var(--secondary);
}

.resource-item-disabled {
    color: var(--text-muted);
    font-weight: 500;
    cursor: default;
}

.resource-card-upcoming {
    background: color-mix(in srgb, var(--bg-card) 75%, var(--bg-secondary));
    border-style: dashed;
}

.case-study-box-muted {
    border-style: dashed;
    background: var(--bg-secondary);
}

/* Enriched reference pages */
.reference-summary {
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    gap: 0.65rem;
    margin: -1.25rem auto 2.25rem;
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.reference-summary span {
    display: inline-flex;
    align-items: center;
    gap: 0.25rem;
    padding: 0.45rem 0.8rem;
    border: 1px solid var(--border-color);
    border-radius: 999px;
    background: var(--bg-card);
}

.reference-meta {
    display: flex;
    justify-content: space-between;
    align-items: flex-end;
    flex-wrap: wrap;
    gap: 0.75rem;
    margin-top: 1.25rem;
    padding-top: 1rem;
    border-top: 1px solid var(--border-color);
    color: var(--text-muted);
    font-size: 0.78rem;
}

.chapter-links {
    display: flex;
    flex-wrap: wrap;
    gap: 0.4rem;
}

.chapter-links a,
.chapter-links span {
    color: var(--text-secondary);
    font-weight: 600;
}

.chapter-links a:hover {
    color: var(--primary);
}

@media (max-width: 600px) {
    .reference-summary {
        align-items: stretch;
        flex-direction: column;
        margin-top: -1.5rem;
    }

    .reference-summary span {
        justify-content: center;
    }

    .reference-meta {
        align-items: flex-start;
        flex-direction: column;
    }
}

.badge-soon {
    font-size: 0.7rem;
    padding: 0.15rem 0.4rem;
    background: rgba(148, 163, 184, 0.08);
    border: 1px solid rgba(148, 163, 184, 0.15);
    color: var(--text-muted);
    border-radius: 4px;
    font-weight: 600;
    margin-left: 0.5rem;
    vertical-align: middle;
}

/* Button & Badge Utility Classes */
.btn-nav-amazon {
    padding: 0.5rem 1rem;
}

.badge-beta {
    display: inline-flex;
    align-items: center;
    gap: 0.35rem;
    padding: 0.2rem 0.65rem;
    background: rgba(249, 115, 22, 0.12);
    border: 1px solid rgba(249, 115, 22, 0.4);
    color: var(--orange);
    font-size: 0.75rem;
    font-weight: 700;
    border-radius: 99px;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    vertical-align: middle;
}

.hero-tagline {
    font-size: 1.4rem;
    font-weight: 500;
    color: var(--text-primary);
    margin-bottom: 1rem;
}

.book-card .title {
    font-size: 1.8rem;
}

.book-card .subtitle {
    font-size: 0.85rem;
    color: #cbd5e1;
    line-height: 1.3;
}

.book-card-footer {
    font-size: 0.75rem;
    color: #94a3b8;
    font-weight: 500;
}

.stats {
    grid-template-columns: repeat(5, minmax(0, 1fr));
}

.author-avatar {
    overflow: hidden;
    padding: 0;
}

.author-avatar-img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    object-position: 50% 15%;
    border-radius: 50%;
}

.author-bio-muted {
    color: var(--text-muted);
    font-size: 0.9rem;
    margin-bottom: 1.5rem;
}

.hero-content .author-bio-muted {
    font-size: 0.95rem;
    color: var(--text-secondary);
    opacity: 0.85;
    margin-top: -1.5rem;
    margin-bottom: 2.5rem;
    max-width: 540px;
    line-height: 1.5;
}

.btn-linkedin-follow {
    display: inline-flex;
    align-items: center;
    gap: 0.75rem;
    font-size: 1.1rem;
    padding: 1rem 2rem;
}

/* Footer */
footer {
    border-top: 1px solid var(--border-color);
    padding: 4rem 2rem;
    background: #f1f5f9;
}

.footer-container {
    max-width: var(--max-width);
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 2rem;
}

.footer-copy {
    color: var(--text-muted);
    font-size: 0.85rem;
}

.footer-links {
    display: flex;
    gap: 1.5rem;
    align-items: center;
}

.footer-links a {
    color: var(--text-muted);
    font-size: 0.85rem;
    text-decoration: none;
    transition: color 0.2s ease;
}

.footer-links a:hover {
    color: var(--primary);
    text-decoration: underline;
}

.resources-notice {
    display: inline-flex;
    align-items: center;
    gap: 0.65rem;
    background: rgba(37, 99, 235, 0.03);
    border: 1px solid rgba(37, 99, 235, 0.15);
    padding: 0.75rem 1.25rem;
    border-radius: 8px;
    font-size: 0.9rem;
    color: var(--text-secondary);
    max-width: 700px;
    margin: 1.5rem auto 0;
    text-align: left;
}

.resources-notice .notice-icon {
    color: var(--primary);
    flex-shrink: 0;
}

/* Responsive adjustments */
@media (max-width: 1024px) {
    .hero {
        grid-template-columns: 1fr;
        text-align: center;
        gap: 3rem;
    }

    .hero-content p {
        margin: 0 auto 2.5rem;
    }

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

    .stats {
        grid-template-columns: repeat(3, minmax(0, 1fr));
    }

    .toc-layout {
        grid-template-columns: 1fr;
    }

    .details-panel {
        position: static;
        min-height: auto;
    }
}

@media (max-width: 768px) {
    .nav-container {
        padding: 1rem 1.5rem;
        flex-direction: row;
        align-items: center;
        gap: 1rem;
    }

    .nav-menu-toggle {
        display: inline-flex;
        margin-left: auto;
    }

    .nav-links {
        position: absolute;
        top: 100%;
        right: 1rem;
        display: none;
        width: min(320px, calc(100vw - 2rem));
        padding: 0.75rem;
        gap: 0.35rem;
        flex-direction: column;
        align-items: stretch;
        background: rgba(248, 250, 252, 0.98);
        border: 1px solid var(--border-color);
        border-radius: 12px;
        box-shadow: var(--shadow-lg);
    }

    .nav-links.is-open {
        display: flex;
    }

    .nav-links a {
        display: block;
        padding: 0.7rem 0.8rem;
        font-size: 0.85rem;
    }

    .nav-links a.btn {
        padding: 0.55rem 0.8rem;
        font-size: 0.82rem;
    }

    .hero {
        padding: 7.5rem 2rem 4rem;
        gap: 2rem;
    }

    .hero-content h1 {
        font-size: 3rem;
    }

    .hero-btns {
        align-items: stretch;
        flex-direction: column;
        max-width: 320px;
        margin: 0 auto;
    }

    .hero-book-wrap img {
        max-width: 220px !important;
    }

    .resources-hero {
        padding-top: 8rem !important;
    }

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

    .author-card {
        grid-template-columns: 1fr;
        text-align: center;
    }

    .stats {
        grid-template-columns: repeat(2, minmax(0, 1fr));
        gap: 1.5rem;
    }

    .stats .stat-item:last-child:nth-child(odd) {
        grid-column: 1 / -1;
        justify-self: center;
        width: calc(50% - 0.75rem);
    }
}

@media (max-width: 480px) {
    .logo {
        font-size: 1.15rem;
    }

    .nav-links {
        gap: 0.35rem;
    }

    .hero {
        padding: 7.25rem 1.25rem 3.5rem;
    }

    .resources-hero {
        padding-top: 7.75rem !important;
    }

    .resources-hero h1 {
        font-size: 2.35rem !important;
        line-height: 1.15;
    }

    .resources-hero p {
        font-size: 1rem !important;
        margin-bottom: 2rem !important;
    }

    .hero-content h1 {
        font-size: 2.7rem;
    }

    .hero-tagline {
        font-size: 1.15rem;
    }

    .btn {
        width: 100%;
        min-height: 48px;
        white-space: normal;
        text-align: center;
    }
}