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

:root {
    --bg-primary: #0F1419;
    --bg-secondary: #151B22;
    --bg-card: #1A2129;
    --bg-input: #1E2732;
    --accent: #00ACED;
    --accent-hover: #38BDF8;
    --text-primary: #E7E9EA;
    --text-secondary: #8B98A5;
    --text-muted: #6B7280;
    --border: #2F3940;
    --success: #00BA7C;
    --warning: #FFAD1F;
    --radius: 8px;
    --radius-lg: 12px;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    background-color: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 24px;
}

a {
    color: var(--accent);
    text-decoration: none;
    transition: color 0.2s;
}

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

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

/* ===== Buttons ===== */
.btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 12px 24px;
    border-radius: var(--radius);
    font-weight: 600;
    font-size: 0.95rem;
    cursor: pointer;
    transition: all 0.2s;
    border: none;
    text-decoration: none;
    font-family: inherit;
}

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

.btn-primary:hover {
    background: var(--accent-hover);
    color: #fff;
    transform: translateY(-1px);
}

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

.btn-secondary:hover {
    background: rgba(0, 172, 237, 0.1);
    color: var(--accent-hover);
    border-color: var(--accent-hover);
}

.btn-sm {
    padding: 8px 16px;
    font-size: 0.85rem;
    border-radius: 6px;
    background: var(--accent);
    color: #fff;
    font-weight: 600;
}

.btn-sm:hover {
    background: var(--accent-hover);
    color: #fff;
}

/* ===== Header ===== */
.site-header {
    position: sticky;
    top: 0;
    z-index: 100;
    background: rgba(15, 20, 25, 0.9);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--border);
}

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

.logo {
    font-weight: 700;
    font-size: 1.1rem;
    color: var(--text-primary);
}

.logo:hover {
    color: var(--accent);
}

.site-header nav {
    display: flex;
    align-items: center;
    gap: 24px;
}

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

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

/* ===== Hero ===== */
.hero {
    padding: 80px 0 100px;
}

.hero-grid {
    display: grid;
    grid-template-columns: 300px 1fr;
    gap: 64px;
    align-items: center;
}

.cover-image {
    width: 100%;
    border-radius: var(--radius-lg);
    box-shadow: 0 25px 60px rgba(0, 0, 0, 0.5), 0 0 40px rgba(0, 172, 237, 0.1);
}

.hero-content h1 {
    font-size: 2.8rem;
    font-weight: 700;
    line-height: 1.15;
    margin-bottom: 12px;
}

.accent {
    color: var(--accent);
}

.subtitle {
    font-size: 1.2rem;
    color: var(--text-secondary);
    margin-bottom: 32px;
}

.stats {
    display: flex;
    gap: 40px;
    margin-bottom: 32px;
}

.stat {
    display: flex;
    flex-direction: column;
}

.stat-number {
    font-size: 2.4rem;
    font-weight: 700;
    color: var(--accent);
    font-family: 'JetBrains Mono', monospace;
    line-height: 1;
}

.stat-label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-top: 4px;
}

.hero-description {
    color: var(--text-secondary);
    font-size: 1.05rem;
    margin-bottom: 32px;
    max-width: 520px;
}

.hero-actions {
    display: flex;
    gap: 16px;
    margin-bottom: 16px;
}

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

/* ===== About the Book ===== */
.about-book {
    padding: 80px 0;
    background: var(--bg-secondary);
}

.about-book h2 {
    font-size: 2rem;
    margin-bottom: 20px;
}

.about-book-text {
    color: var(--text-secondary);
    font-size: 1.15rem;
    line-height: 1.75;
    max-width: 720px;
}

.section-intro {
    color: var(--text-secondary);
    font-size: 1.05rem;
    max-width: 640px;
    margin-bottom: 48px;
}

/* ===== Tiers (exercises page) ===== */
.tier-badge {
    background: rgba(0, 172, 237, 0.15);
    color: var(--accent);
    font-size: 0.75rem;
    font-weight: 600;
    padding: 4px 10px;
    border-radius: 4px;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

/* ===== Projects ===== */
.projects {
    padding: 80px 0;
}

.projects h2 {
    font-size: 2rem;
    margin-bottom: 12px;
}

.project-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 24px;
}

.project-grid .project-card:nth-child(4),
.project-grid .project-card:nth-child(5) {
    /* Center the last two cards in a 3-col grid */
}

.project-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    overflow: hidden;
    transition: border-color 0.2s;
}

.project-card:hover {
    border-color: var(--accent);
}

.project-screenshot {
    background: var(--bg-input);
    height: 180px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-bottom: 1px solid var(--border);
    overflow: hidden;
}

.project-screenshot img {
    width: 100%;
    height: 100%;
    object-fit: cover;
}

.project-screenshot span {
    color: var(--text-muted);
    font-size: 0.85rem;
}

.project-info {
    padding: 20px 24px;
}

.project-info h3 {
    font-size: 1.1rem;
    margin-bottom: 6px;
}

.project-info p {
    color: var(--text-secondary);
    font-size: 0.9rem;
    margin-bottom: 12px;
}

.project-link {
    font-size: 0.85rem;
    font-weight: 600;
}

/* ===== Author ===== */
.author {
    padding: 80px 0;
    background: var(--bg-secondary);
}

.author h2 {
    font-size: 2rem;
    margin-bottom: 20px;
}

.author-layout {
    display: flex;
    align-items: flex-start;
    gap: 48px;
}

.author-photo-wrap {
    flex-shrink: 0;
    width: 160px;
    height: 160px;
    border-radius: 50%;
    overflow: hidden;
    border: 3px solid var(--accent);
    box-shadow: 0 0 24px rgba(0, 172, 237, 0.15);
}

.author-photo {
    width: 100%;
    height: 100%;
    object-fit: cover;
    object-position: center;
    display: block;
}

.author-content p {
    color: var(--text-secondary);
    font-size: 1.05rem;
    margin-bottom: 16px;
    max-width: 700px;
}

.author-content strong {
    color: var(--text-primary);
}

/* ===== Book Access ===== */
.book-access {
    padding: 80px 0;
    text-align: center;
}

.book-access h2 {
    font-size: 2rem;
    margin-bottom: 12px;
}

.book-access p {
    color: var(--text-secondary);
    font-size: 1.05rem;
    margin-bottom: 32px;
}

/* ===== Footer ===== */
.site-footer {
    padding: 32px 0;
    border-top: 1px solid var(--border);
    text-align: center;
}

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

.footer-links {
    margin-top: 8px;
}

.footer-links a {
    color: var(--text-secondary);
    font-size: 0.85rem;
}

.footer-sep {
    color: var(--text-muted);
    margin: 0 8px;
}

/* ===== Auth Gate ===== */
.auth-gate {
    min-height: calc(100vh - 64px);
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 40px 24px;
}

.auth-box {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 48px;
    max-width: 420px;
    width: 100%;
    text-align: center;
}

.auth-box h2 {
    font-size: 1.5rem;
    margin-bottom: 8px;
}

.auth-box .auth-subtitle {
    color: var(--text-secondary);
    font-size: 0.95rem;
    margin-bottom: 32px;
}

.auth-box input[type="text"] {
    width: 100%;
    padding: 12px 16px;
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    color: var(--text-primary);
    font-family: 'JetBrains Mono', monospace;
    font-size: 1rem;
    text-align: center;
    letter-spacing: 0.15em;
    margin-bottom: 16px;
    outline: none;
    transition: border-color 0.2s;
}

.auth-box input[type="text"]:focus {
    border-color: var(--accent);
}

.auth-box input[type="text"]::placeholder {
    color: var(--text-muted);
    letter-spacing: 0.05em;
}

.auth-box .btn {
    width: 100%;
    justify-content: center;
}

.auth-error {
    color: #EF4444;
    font-size: 0.85rem;
    margin-top: 12px;
    display: none;
}

.auth-hint {
    color: var(--text-muted);
    font-size: 0.8rem;
    margin-top: 20px;
}

/* ===== Exercises Page ===== */
.exercises-page {
    padding: 48px 0 80px;
}

.exercises-page h1 {
    font-size: 2rem;
    margin-bottom: 8px;
}

.exercises-intro {
    color: var(--text-secondary);
    font-size: 1.05rem;
    margin-bottom: 48px;
    max-width: 640px;
}

.tier-section {
    margin-bottom: 48px;
}

.tier-section-header {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 20px;
    padding-bottom: 12px;
    border-bottom: 1px solid var(--border);
}

.tier-section-header h2 {
    font-size: 1.3rem;
}

.exercise-list {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.exercise-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 20px 24px;
    display: flex;
    align-items: flex-start;
    gap: 16px;
}

.exercise-card.coming-soon {
    opacity: 0.5;
}

.exercise-number {
    background: rgba(0, 172, 237, 0.15);
    color: var(--accent);
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.8rem;
    font-weight: 600;
    padding: 4px 8px;
    border-radius: 4px;
    white-space: nowrap;
    min-width: 36px;
    text-align: center;
}

.exercise-info h3 {
    font-size: 1rem;
    margin-bottom: 4px;
}

.exercise-info p {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.coming-soon-badge {
    font-size: 0.75rem;
    color: var(--text-muted);
    background: rgba(107, 114, 128, 0.2);
    padding: 2px 8px;
    border-radius: 4px;
    margin-left: auto;
    white-space: nowrap;
}

/* ===== Downloads Page ===== */
.downloads-page {
    padding: 48px 0 80px;
}

.downloads-page h1 {
    font-size: 2rem;
    margin-bottom: 8px;
}

.downloads-intro {
    color: var(--text-secondary);
    font-size: 1.05rem;
    margin-bottom: 48px;
    max-width: 640px;
}

.download-cards {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
    gap: 24px;
}

.download-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 28px;
}

.download-card h3 {
    font-size: 1.1rem;
    margin-bottom: 8px;
}

.download-card p {
    color: var(--text-secondary);
    font-size: 0.9rem;
    margin-bottom: 20px;
}

.download-card .btn {
    width: 100%;
    justify-content: center;
}

.file-type {
    color: var(--text-muted);
    font-size: 0.8rem;
    font-family: 'JetBrains Mono', monospace;
    margin-top: 8px;
    text-align: center;
}

/* ===== Responsive ===== */
@media (max-width: 768px) {
    .hero {
        padding: 48px 0 64px;
    }

    .hero-grid {
        grid-template-columns: 1fr;
        gap: 40px;
        text-align: center;
    }

    .hero-cover {
        max-width: 220px;
        margin: 0 auto;
    }

    .hero-content h1 {
        font-size: 2rem;
    }

    .subtitle {
        font-size: 1.05rem;
    }

    .stats {
        justify-content: center;
    }

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

    .project-grid {
        grid-template-columns: 1fr;
        max-width: 440px;
    }

    .author-layout {
        flex-direction: column;
        align-items: center;
        text-align: center;
    }

    .author-photo-wrap {
        width: 120px;
        height: 120px;
    }

    .site-header nav {
        gap: 16px;
    }

    .nav-exercises {
        display: none;
    }

    .auth-box {
        padding: 32px 24px;
    }

    .exercise-card {
        flex-direction: column;
        gap: 8px;
    }

    .coming-soon-badge {
        margin-left: 0;
    }
}

@media (min-width: 769px) and (max-width: 1024px) {
    .project-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 480px) {
    .site-header nav a:not(.btn) {
        display: none;
    }

    .hero-content h1 {
        font-size: 1.7rem;
    }

    .stat-number {
        font-size: 1.8rem;
    }
}