:root {
    /* Design Tokens */
    --bg-page: #ffffff;
    --text-main: #111827;
    --text-body: #374151;
    --text-muted: #6b7280;
    --accent: #2563eb;
    --accent-soft: #eff6ff;
    --border-light: #e5e7eb;

    /* Typography */
    --font-display: 'Inter', sans-serif;
    --font-body: 'Merriweather', serif;
    --font-mono: 'JetBrains Mono', monospace;

    /* Spacing */
    --spacing-container: 1rem;
    --max-width-text: 65ch;
}

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

html {
    scroll-behavior: smooth;
}

body {
    background-color: var(--bg-page);
    color: var(--text-body);
    font-family: var(--font-body);
    line-height: 1.8;
    -webkit-font-smoothing: antialiased;
}

/* Typography Overrides */
h1,
h2,
h3,
h4,
.nav-back,
footer,
.caption,
.toc-title,
.toc-link,
.faq-question {
    font-family: var(--font-display);
    color: var(--text-main);
}

a {
    text-decoration: none;
    color: inherit;
    transition: color 0.2s;
}

/* Navigation Bar */
.page-nav {
    padding: 1.5rem 1rem;
    position: sticky;
    top: 0;
    background: rgba(255, 255, 255, 0.9);
    backdrop-filter: blur(8px);
    z-index: 100;
    border-bottom: 1px solid transparent;
    transition: border-color 0.3s;
}

@media (max-width: 600px) {
    .page-nav {
        padding: 1rem;
    }

    .page-nav>div {
        flex-direction: column;
        align-items: flex-start !important;
        gap: 0.75rem;
    }

    .nav-back {
        font-size: 0.8rem;
    }
}

.nav-back {
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--text-muted);
}

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

/* Common Content Elements */
header {
    margin-bottom: 4rem;
}

h1 {
    font-size: clamp(2.5rem, 4vw, 3.5rem);
    font-weight: 800;
    line-height: 1.2;
    letter-spacing: -0.02em;
    margin-bottom: 1rem;
}

.subtitle {
    font-size: 1.25rem;
    color: var(--text-muted);
    font-family: var(--font-display);
    font-weight: 400;
}

p {
    margin-bottom: 1.5rem;
    font-size: 1.125rem;
    font-weight: 300;
}

h2 {
    font-size: 1.75rem;
    margin-top: 3rem;
    margin-bottom: 1rem;
    letter-spacing: -0.01em;
    scroll-margin-top: 6rem;
}

h3 {
    font-size: 1.4rem;
    margin-top: 2rem;
    margin-bottom: 0.75rem;
}

ul,
ol {
    margin-bottom: 2rem;
    padding-left: 1.5rem;
}

li {
    margin-bottom: 0.75rem;
}

strong {
    font-weight: 700;
    color: var(--text-main);
}

em {
    color: var(--text-main);
}

/* Math & Code Blocks */
.math {
    font-family: var(--font-mono);
    background: var(--accent-soft);
    padding: 0.2em 0.4em;
    border-radius: 4px;
    font-size: 0.9em;
}

.math-block {
    font-family: var(--font-mono);
    background: #f8fafc;
    padding: 1.5rem;
    border-radius: 8px;
    margin: 2rem 0;
    overflow-x: auto;
    border-left: 3px solid var(--accent);
    font-size: 0.95em;
    line-height: 1.6;
}

/* Custom Highlight Boxes */
.highlight-box {
    background-color: var(--accent-soft);
    border-radius: 8px;
    padding: 2rem;
    margin: 2.5rem 0;
    font-family: var(--font-display);
    font-size: 1rem;
    border-left: 4px solid var(--accent);
}

.highlight-box p:last-child {
    margin-bottom: 0;
}

.analogy {
    background-color: #f0fdf4;
    /* Soft green */
    padding: 1.5rem;
    border-left: 4px solid #10b981;
    border-radius: 4px;
    margin: 1.5rem 0;
    font-style: italic;
    font-family: var(--font-display);
}

.tech-context {
    background-color: #f8fafc;
    /* Slate 50 */
    padding: 1rem;
    border-radius: 4px;
    font-size: 0.95em;
    margin-bottom: 1.5rem;
    font-family: var(--font-display);
    color: var(--text-muted);
}

/* FAQ Section */
.faq-item {
    margin-bottom: 2rem;
    border-bottom: 1px solid var(--border-light);
    padding-bottom: 1rem;
}

.faq-question {
    font-weight: 600;
    font-size: 1.2rem;
    margin-bottom: 0.5rem;
    display: block;
}

/* Reference Linking */
.ref-link {
    color: var(--accent);
    text-decoration: underline;
    text-decoration-color: rgba(37, 99, 235, 0.3);
    text-underline-offset: 2px;
}

.ref-link:hover {
    color: #1d4ed8;
    text-decoration-color: #1d4ed8;
}

/* Cross Navigation */
.cross-nav {
    display: flex;
    gap: 1rem;
    margin: 2rem 0;
    padding: 1.5rem;
    background: var(--accent-soft);
    border-radius: 8px;
    font-family: var(--font-display);
}

@media (max-width: 600px) {
    .cross-nav {
        flex-direction: column;
        padding: 1rem;
    }

    .nav-link {
        width: 100%;
        min-height: 3rem;
    }
}

.cross-nav.bottom {
    margin-top: 4rem;
}

.nav-link {
    flex: 1;
    min-width: 120px;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 0.75rem 1rem;
    background: white;
    border-radius: 6px;
    font-size: 0.9rem;
    font-weight: 500;
    color: var(--text-main);
    border: 1px solid var(--border-light);
    transition: all 0.2s;
}

.nav-link img {
    display: inline-block !important;
    margin: 0 0.4rem 0 0 !important;
    box-shadow: none !important;
    border-radius: 0 !important;
}

.nav-link:hover {
    border-color: var(--accent);
    color: var(--accent);
    transform: translateY(-2px);
    box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
}

/* Universal Footer */
.article-footer {
    margin-top: 6rem;
    padding-top: 2rem;
    text-align: center;
    border-top: 1px solid var(--border-light);
    font-size: 0.875rem;
    color: var(--text-muted);
    font-family: var(--font-display);
}