:root {
    /* ===== BASE COLORS ===== */
    --bg-background: #0d1117;
    --bg-card: #1c2128;
    --bg-muted: #161b22;

    /* ===== TEXT COLORS (WCAG AA Compliant) ===== */
    --text-foreground: #f0f6fc;
    --text-muted-foreground: #9ca3af;
    --text-accent: #ffa94d;
    /* Java Orange */
    --text-primary: #79c0ff;
    /* Java Blue */

    /* ===== BORDERS ===== */
    --border-border: #3d444d;
    --border-subtle: #21262d;

    /* ===== FUNCTIONAL COLORS ===== */
    --color-success: #3fb950;
    --color-warning: #e3b341;
    --color-danger: #ff7b72;
    --color-info: #58a6ff;

    /* ===== SYNTAX HIGHLIGHTING ===== */
    --syntax-kw: #ff9e64;
    /* Keywords */
    --syntax-type: #f7d88c;
    /* Types */
    --syntax-str: #a5d6ff;
    /* Strings */
    --syntax-num: #79c0ff;
    /* Numbers */
    --syntax-com: #9ca3af;
    /* Comments */
    --syntax-anno: #d2a8ff;
    /* Annotations */

    /* ===== MERMAID DIAGRAM COLORS ===== */
    /* Use these in Mermaid diagrams for consistency */
    --mermaid-bg-dark: #0d1117;
    /* Dark background */
    --mermaid-bg-card: #1c2128;
    /* Card background */
    --mermaid-accent: #ffa94d;
    /* Orange (highlight) */
    --mermaid-primary: #79c0ff;
    /* Blue (primary) */
    --mermaid-success: #3fb950;
    /* Green (success) */
    --mermaid-danger: #ff7b72;
    /* Red (danger) */
    --mermaid-warning: #e3b341;
    /* Yellow (warning) */
    --mermaid-text-light: #f0f6fc;
    /* Light text */
    --mermaid-text-dark: #0d1117;
    /* Dark text (for light backgrounds) */
    --mermaid-border: #3d444d;
    /* Borders */

    /* ===== TYPOGRAPHY ===== */
    --font-main: 'Outfit', sans-serif;
    --font-code: 'JetBrains Mono', monospace;
    --font-size-base: 17px;
    --line-height-base: 1.7;
}

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

html {
    scroll-behavior: smooth;
}

body {
    background-color: var(--bg-background);
    color: var(--text-foreground);
    font-family: var(--font-main);
    font-size: var(--font-size-base);
    line-height: var(--line-height-base);
    overflow-x: hidden;
}

/* Header */
header {
    background: rgba(13, 17, 23, 0.95);
    /* Keep strict value for transparency, or use var with opacity if needed in future */
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--border-border);
    position: sticky;
    top: 0;
    z-index: 1000;
    padding: 1rem 0;
}

.container {
    max-width: 1000px;
    margin: 0 auto;
    padding: 0 20px;
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    font-weight: 700;
    font-size: 1.5rem;
    display: flex;
    align-items: center;
    gap: 10px;
    color: var(--text-foreground);
}

.logo-icon {
    color: var(--text-accent);
    font-size: 1.8rem;
}

nav {
    display: flex;
    gap: 20px;
}

nav a {
    color: var(--text-foreground);
    text-decoration: none;
    font-weight: 500;
    font-size: 0.9rem;
    opacity: 0.8;
    transition: all 0.2s;
}

nav a:hover {
    color: var(--text-accent);
    opacity: 1;
}

/* Hero */
.hero {
    padding: 4rem 0;
    text-align: center;
    background: radial-gradient(circle at center, rgba(83, 130, 161, 0.15) 0%, transparent 70%);
}

h1 {
    font-size: 3.5rem;
    margin-bottom: 1rem;
    background: linear-gradient(135deg, #fff 0%, var(--text-primary) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero p {
    font-size: 1.25rem;
    color: var(--text-muted-foreground);
    max-width: 650px;
    margin: 0 auto;
    line-height: 1.8;
}

/* Sections */
section {
    padding: 3rem 0;
    border-bottom: 1px solid var(--border-border);
}

.sec-header {
    display: flex;
    align-items: flex-start;
    gap: 20px;
    margin-bottom: 2rem;
}

.sec-num {
    font-family: var(--font-code);
    font-size: 3rem;
    font-weight: 700;
    color: rgba(255, 255, 255, 0.05);
    /* Semantic Issue: Low opacity white for "watermark" style can stay, or use muted/0.1 */
    line-height: 1;
}

.sec-title {
    font-size: 2rem;
    margin-bottom: 0.2rem;
    color: var(--text-foreground);
}

.sec-sub {
    color: var(--text-accent);
    font-family: var(--font-code);
    font-size: 0.9rem;
    text-transform: uppercase;
    letter-spacing: 1px;
}

/* Details/Summary */
details {
    background: var(--bg-card);
    border: 1px solid var(--border-border);
    border-radius: 8px;
    margin-bottom: 2rem;
    overflow: hidden;
}

summary {
    padding: 1rem 1.5rem;
    cursor: pointer;
    font-weight: 600;
    background: rgba(255, 255, 255, 0.02);
    display: flex;
    align-items: center;
    gap: 10px;
    transition: background 0.2s;
    list-style: none;
}

summary::-webkit-details-marker {
    display: none;
}

summary:hover {
    background: rgba(255, 255, 255, 0.05);
}

details[open] summary {
    border-bottom: 1px solid var(--border-border);
    color: var(--text-accent);
}

details>div {
    padding: 1.5rem;
    line-height: 1.7;
    color: var(--text-foreground);
    /* Was #c9d1d9, close to foreground */
}

details p+p {
    margin-top: 1rem;
}

strong {
    color: #fff;
    /* Could be --text-foreground or keep bright white for emphasis */
    font-weight: 600;
}

/* Code Blocks */
.grid2 {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 20px;
}

.grid3 {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 20px;
}

.code {
    background: var(--bg-muted);
    border: 1px solid var(--border-border);
    border-radius: 8px;
    overflow: hidden;
    position: relative;
    transition: transform 0.2s, border-color 0.2s;
}

.code:hover {
    border-color: var(--text-primary);
}

.code-head {
    padding: 8px 15px;
    background: rgba(0, 0, 0, 0.3);
    font-family: var(--font-code);
    font-size: 0.75rem;
    color: var(--text-muted-foreground);
    border-bottom: 1px solid var(--border-border);
    display: flex;
    align-items: center;
    gap: 8px;
}

.dot {
    width: 8px;
    height: 8px;
    border-radius: 50%;
    display: inline-block;
}

.dot.r {
    background: var(--text-accent);
}

.dot.b {
    background: var(--text-primary);
}

.dot.g {
    background: var(--text-foreground);
}

pre {
    padding: 15px;
    font-family: var(--font-code);
    font-size: 0.85rem;
    color: var(--text-foreground);
    overflow-x: auto;
    white-space: pre;
}

/* Syntax Highlighting */
.kw {
    color: var(--syntax-kw);
    font-weight: bold;
}

.type {
    color: var(--syntax-type);
    font-weight: bold;
}

.str {
    color: var(--syntax-str);
}

.num {
    color: var(--syntax-num);
}

.com {
    color: var(--syntax-com);
    font-style: italic;
}

.anno {
    color: var(--syntax-anno);
}

.mt {
    color: var(--syntax-anno);
}

/* Footer */
footer {
    padding: 3rem 0;
    text-align: center;
    color: var(--text-muted-foreground);
    border-top: 1px solid var(--border-border);
    margin-top: 4rem;
}

/* Utilities */
.tip {
    background: rgba(83, 130, 161, 0.1);
    border-left: 3px solid var(--text-primary);
    padding: 1rem;
    border-radius: 4px;
    font-size: 0.9rem;
    color: var(--text-foreground);
}

.intro-box {
    background: var(--bg-card) !important;
    border-bottom: 1px solid var(--border-border) !important;
    padding: 30px 0;
}

.intro-box h3 {
    margin-top: 0;
    color: var(--text-foreground) !important;
}

.intro-box p {
    color: var(--text-foreground) !important;
    opacity: 0.9;
}

/* Tool Cards (New) */
.tool-card {
    background: var(--bg-card);
    border: 1px solid var(--border-border);
    padding: 1.5rem;
    border-radius: 8px;
    transition: transform 0.2s;
}

.tool-card:hover {
    transform: translateY(-3px);
    border-color: var(--text-accent);
}

.tool-icon {
    font-size: 2rem;
    display: block;
    margin-bottom: 1rem;
}

.tool-card h3 {
    color: var(--text-foreground);
    margin-bottom: 0.5rem;
}

.tool-card p {
    color: var(--text-muted-foreground);
    font-size: 0.9rem;
}


/* Responsive */
@media (max-width: 768px) {
    .grid2 {
        grid-template-columns: 1fr;
    }
}

/* --- Pedagogical Modules --- */

/* Callouts - Enhanced Spacing */
.callout {
    padding: 2rem 2.25rem;
    border-radius: 12px;
    margin: 2.5rem 0;
    border-left: 6px solid;
    background: var(--bg-card);
    position: relative;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
}

.callout h4 {
    margin-top: 0;
    margin-bottom: 1rem;
    display: flex;
    align-items: center;
    gap: 12px;
    font-size: 1.2rem;
    color: var(--text-foreground);
    font-weight: 600;
}

.callout p {
    color: var(--text-foreground);
    line-height: 1.8;
    margin-bottom: 1rem;
}

.callout *:last-child {
    margin-bottom: 0;
}

.callout-info {
    border-color: var(--color-info);
    background: linear-gradient(90deg, rgba(88, 166, 255, 0.15), var(--bg-card));
}

.callout-warning {
    border-color: var(--color-warning);
    background: linear-gradient(90deg, rgba(227, 179, 65, 0.15), var(--bg-card));
}

.callout-tip {
    border-color: var(--color-success);
    background: linear-gradient(90deg, rgba(63, 185, 80, 0.15), var(--bg-card));
}

.callout-recall {
    border-color: var(--text-accent);
    border-style: dashed;
    background: linear-gradient(90deg, rgba(255, 169, 77, 0.1), var(--bg-card));
}

/* Analogy Block - Enhanced */
.analogy {
    background: linear-gradient(135deg, rgba(255, 169, 77, 0.08) 0%, var(--bg-muted) 100%);
    border: 2px solid rgba(255, 169, 77, 0.3);
    border-radius: 12px;
    padding: 2.5rem;
    margin: 2.5rem 0;
    text-align: center;
    position: relative;
    overflow: hidden;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
}

.analogy::before {
    content: "💡 ANALOGIE";
    display: block;
    font-family: var(--font-code);
    font-size: 0.85rem;
    color: var(--text-accent);
    margin-bottom: 1.25rem;
    letter-spacing: 2px;
    font-weight: bold;
    text-transform: uppercase;
}

.analogy p {
    font-size: 1.15rem;
    font-style: italic;
    color: var(--text-foreground);
    line-height: 1.8;
    margin-bottom: 0.75rem;
}

/* Use Case Block - Enhanced */
.use-case {
    background: linear-gradient(180deg, rgba(88, 166, 255, 0.08) 0%, var(--bg-card) 100%);
    border: 2px solid rgba(88, 166, 255, 0.25);
    border-radius: 12px;
    padding: 2.25rem 2.5rem;
    margin: 3rem 0;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
}

.use-case *:last-child,
.analogy *:last-child {
    margin-bottom: 0;
}

.use-case h4 {
    color: var(--text-foreground);
    border-bottom: 2px solid var(--color-info);
    padding-bottom: 0.75rem;
    margin-bottom: 1.25rem;
    font-family: var(--font-code);
    font-size: 1.1rem;
}

.use-case p,
.use-case ul {
    color: var(--text-foreground);
    line-height: 1.8;
}

/* Diagram Container - DARK THEME for readability */
.diagram-container {
    background: var(--bg-card);
    padding: 20px;
    border-radius: 8px;
    margin: 20px 0;
    text-align: center;
    overflow-x: auto;
    border: 1px solid var(--border-border);
    /* Dark background ensures Mermaid text is readable */
}

/* Details Animation */
details[open] summary~* {
    animation: sweep .3s ease-in-out;
}

@keyframes sweep {
    0% {
        opacity: 0;
        transform: translateY(-10px)
    }

    100% {
        opacity: 1;
        transform: translateY(0)
    }
}/* Back to Top Button */
#backToTop {
    position: fixed;
    bottom: 30px;
    right: 30px;
    background: var(--color-info);
    color: white;
    width: 50px;
    height: 50px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.5rem;
    cursor: pointer;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
    opacity: 0;
    visibility: hidden;
    transform: translateY(20px);
    transition: all 0.3s ease;
    z-index: 9999;
    border: none;
}

#backToTop.visible {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

#backToTop:hover {
    background: var(--text-primary);
    transform: translateY(-5px);
}

/* Scroll Progress Bar */
#scrollProgress {
    position: fixed;
    top: 0;
    left: 0;
    width: 0%;
    height: 3px;
    background: linear-gradient(90deg, var(--color-info), var(--color-success));
    z-index: 1001;
    transition: width 0.1s;
}

/* Animations Classes */
.fade-in-section {
    opacity: 0;
    transform: translateY(20px);
    transition: opacity 0.6s ease-out, transform 0.6s ease-out;
    will-change: opacity, visibility;
}

.fade-in-section.is-visible {
    opacity: 1;
    transform: none;
}

/* Hover Effects Enhancements */
.sec-title {
    transition: color 0.3s;
}

.sec-header:hover .sec-title {
    color: var(--text-primary);
}

.analogy,
.use-case,
.callout {
    transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.analogy:hover,
.use-case:hover,
.callout:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.4);
}

/* TOC Sidebar */
#toc-sidebar {
    position: fixed;
    top: 100px;
    left: 20px;
    width: 220px;
    max-height: calc(100vh - 120px);
    overflow-y: auto;
    background: rgba(13, 17, 23, 0.9);
    backdrop-filter: blur(5px);
    border: 1px solid var(--border-border);
    border-radius: 8px;
    padding: 1rem;
    z-index: 900;
    display: none;
    scrollbar-width: thin;
    scrollbar-color: var(--border-border) transparent;
}

@media (min-width: 1400px) {
    #toc-sidebar {
        display: block;
    }
}

#toc-sidebar ul {
    list-style: none;
}

#toc-sidebar li {
    margin-bottom: 0.5rem;
}

#toc-sidebar a {
    display: block;
    color: var(--text-muted-foreground);
    text-decoration: none;
    font-size: 0.85rem;
    transition: all 0.2s;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

#toc-sidebar a:hover {
    color: var(--text-foreground);
    padding-left: 5px;
}

#toc-sidebar a.active {
    color: var(--text-accent);
    font-weight: bold;
    border-left: 2px solid var(--text-accent);
    padding-left: 8px;
}