/*
 * Cyber Security Study Guide - Professional Stylesheet
 * Clean, refined, editorial design for extended study sessions
 * With Dark Mode, Animations, and Interactive Features
 */

/* ========================================
   CSS VARIABLES (Light Mode)
   ======================================== */
:root {
    /* Primary Colors */
    --bg-primary: #f7f8fa;
    --bg-secondary: #ffffff;
    --bg-tertiary: #eef1f5;
    --bg-accent: #edf2f7;

    /* Text Colors */
    --text-primary: #111827;
    --text-secondary: #1f2937;
    --text-muted: #6b7280;

    /* Brand Colors */
    --brand-primary: #1b2a3d;
    --brand-secondary: #334155;
    --brand-accent: #3d6098;

    /* Border Colors */
    --border-light: #e5e7eb;
    --border-medium: #d1d5db;
    --border-dark: #9ca3af;

    /* Semantic Colors */
    --color-info: #3d6098;
    --color-success: #2f6b4f;
    --color-warning: #92600a;
    --color-warning-bg: #fefce8;
    --color-warning-border: #e5d5a0;

    /* Answer Box */
    --answer-bg: #f0faf4;
    --answer-border: #a7d7be;
    --answer-accent: #2f6b4f;

    /* Interactive Colors */
    --highlight-yellow: rgba(255, 235, 59, 0.5);
    --highlight-green: rgba(76, 175, 80, 0.4);
    --highlight-blue: rgba(33, 150, 243, 0.4);
    --highlight-note: rgba(233, 30, 99, 0.3);

    /* Shadows */
    --shadow-xs: 0 1px 2px rgba(0, 0, 0, 0.04);
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.06), 0 1px 2px rgba(0, 0, 0, 0.04);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.05), 0 2px 4px rgba(0, 0, 0, 0.04);
    --shadow-lg: 0 10px 20px rgba(0, 0, 0, 0.06), 0 4px 8px rgba(0, 0, 0, 0.04);

    /* Radius */
    --radius-sm: 4px;
    --radius-md: 6px;
    --radius-lg: 8px;
}

/* ========================================
   DARK MODE VARIABLES
   ======================================== */
body.dark-mode {
    --bg-primary: #0d1117;
    --bg-secondary: #161b22;
    --bg-tertiary: #1c2128;
    --bg-accent: #1c2333;

    --text-primary: #e6edf3;
    --text-secondary: #c9d1d9;
    --text-muted: #8b949e;

    --brand-primary: #c9d1d9;
    --brand-secondary: #3d6098;
    --brand-accent: #6a9fd8;

    --border-light: #21262d;
    --border-medium: #30363d;
    --border-dark: #484f58;

    --color-info: #6a9fd8;
    --color-success: #56d384;
    --color-warning: #d4a72c;
    --color-warning-bg: #1c1a10;
    --color-warning-border: #3d3520;

    --answer-bg: #0f1d15;
    --answer-border: #1e3a2a;
    --answer-accent: #56d384;

    --shadow-xs: 0 1px 2px rgba(0, 0, 0, 0.2);
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.25);
    --shadow-md: 0 4px 8px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 24px rgba(0, 0, 0, 0.35);
}

/* Theme transition */
body.theme-transitioning,
body.theme-transitioning * {
    transition: background-color 0.3s ease, color 0.3s ease, border-color 0.3s ease !important;
}

/* ========================================
   RESET AND BASE STYLES
   ======================================== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: -apple-system, 'Segoe UI', 'Helvetica Neue', Arial, sans-serif;
    font-size: 16px;
    line-height: 1.75;
    color: var(--text-secondary);
    background-color: var(--bg-primary);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* ========================================
   TYPOGRAPHY HIERARCHY
   ======================================== */
h1, h2, h3, h4, h5, h6 {
    font-family: -apple-system, 'Segoe UI', 'Helvetica Neue', Arial, sans-serif;
    font-weight: 700;
    line-height: 1.3;
    color: var(--text-primary);
    letter-spacing: -0.01em;
}

/* ========================================
   NAVIGATION
   ======================================== */
header {
    background-color: var(--brand-primary);
    position: sticky;
    top: 0;
    z-index: 1000;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.15);
}

.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 32px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.nav-brand {
    color: #ffffff;
    text-decoration: none;
    font-size: 17px;
    font-weight: 700;
    padding: 16px 0;
    letter-spacing: -0.01em;
}

.nav-menu {
    list-style: none;
    display: flex;
    gap: 2px;
}

.nav-menu > li {
    position: relative;
}

.nav-menu a {
    color: rgba(255, 255, 255, 0.8);
    text-decoration: none;
    padding: 16px 18px;
    display: block;
    font-size: 13.5px;
    font-weight: 500;
    letter-spacing: 0.01em;
    transition: color 0.2s ease, background-color 0.2s ease;
    border-bottom: 2px solid transparent;
}

.nav-menu a:hover {
    color: #ffffff;
    background-color: rgba(255, 255, 255, 0.08);
}

.nav-menu a.active {
    color: #ffffff;
    border-bottom-color: #ffffff;
}

/* Dropdown Menu */
.dropdown-menu {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    background-color: var(--bg-secondary);
    list-style: none;
    min-width: 180px;
    border: 1px solid var(--border-light);
    border-radius: 0 0 var(--radius-md) var(--radius-md);
    box-shadow: var(--shadow-lg);
    z-index: 1000;
    overflow: hidden;
}

.dropdown:hover .dropdown-menu {
    display: block;
}

.dropdown-menu a {
    color: var(--text-secondary);
    padding: 11px 20px;
    border-bottom: 1px solid var(--border-light);
    font-size: 13px;
    font-weight: 500;
}

.dropdown-menu li:last-child a {
    border-bottom: none;
}

.dropdown-menu a:hover {
    background-color: var(--bg-tertiary);
    color: var(--text-primary);
}

/* ========================================
   MAIN CONTENT CONTAINER
   ======================================== */
main {
    max-width: 880px;
    margin: 0 auto;
    padding: 48px 32px 72px;
}

/* ========================================
   HERO SECTION
   ======================================== */
.hero {
    text-align: center;
    padding: 64px 0 56px;
    margin-bottom: 48px;
    border-bottom: 1px solid var(--border-light);
}

.hero h1 {
    font-size: 40px;
    font-weight: 800;
    margin-bottom: 16px;
    letter-spacing: -0.02em;
    text-transform: uppercase;
    color: var(--text-primary);
}

.course-codes {
    font-size: 17px;
    font-weight: 500;
    margin-bottom: 8px;
    color: var(--text-muted);
}

.university {
    font-size: 15px;
    font-style: normal;
    color: var(--text-muted);
}

/* ========================================
   UNIT OVERVIEW BLOCK
   ======================================== */
.unit-overview {
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-light);
    border-top: 3px solid var(--brand-primary);
    border-radius: var(--radius-lg);
    padding: 32px 36px;
    margin-bottom: 48px;
    box-shadow: var(--shadow-sm);
}

.unit-overview h2 {
    font-size: 14px;
    font-weight: 700;
    margin-bottom: 16px;
    padding-bottom: 14px;
    border-bottom: 1px solid var(--border-light);
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--color-info);
}

.unit-overview p {
    margin-bottom: 16px;
    line-height: 1.75;
    color: var(--text-secondary);
}

.unit-overview ul {
    margin: 16px 0 0 24px;
}

.unit-overview li {
    margin-bottom: 8px;
    color: var(--text-secondary);
}

/* Topics Covered List */
.topics-covered {
    margin-top: 24px;
    padding-top: 20px;
    border-top: 1px solid var(--border-light);
}

.topics-covered h3 {
    font-size: 11px;
    font-weight: 700;
    margin-bottom: 14px;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--text-muted);
}

.topics-covered ul {
    list-style: none;
    margin: 0;
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
}

.topics-covered li {
    background-color: var(--bg-tertiary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-sm);
    padding: 5px 14px;
    font-size: 13px;
    font-weight: 500;
    color: var(--text-secondary);
}

/* ========================================
   CONTENT SECTIONS
   ======================================== */
.content-section {
    margin-bottom: 56px;
    padding-bottom: 48px;
    border-bottom: 1px solid var(--border-light);
}

.content-section:last-of-type {
    border-bottom: none;
    margin-bottom: 40px;
}

.content-section h2 {
    font-size: 24px;
    font-weight: 700;
    margin-bottom: 24px;
    padding-bottom: 14px;
    border-bottom: 2px solid var(--text-primary);
    color: var(--text-primary);
    letter-spacing: -0.01em;
}

.content-section h3 {
    font-size: 20px;
    font-weight: 600;
    margin: 40px 0 16px 0;
    color: var(--text-primary);
}

.content-section h4 {
    font-size: 17px;
    font-weight: 600;
    margin: 32px 0 14px 0;
    color: var(--text-primary);
}

.content-section p {
    margin-bottom: 18px;
    text-align: justify;
    hyphens: auto;
    color: var(--text-secondary);
    line-height: 1.8;
}

.content-section ul,
.content-section ol {
    margin: 18px 0 18px 28px;
}

.content-section li {
    margin-bottom: 10px;
    line-height: 1.75;
}

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

/* ========================================
   CONTENT BLOCKS / CARDS
   ======================================== */
.content-block {
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-lg);
    padding: 28px 32px;
    margin: 28px 0;
    box-shadow: var(--shadow-xs);
}

.content-block h4 {
    margin-top: 0;
    margin-bottom: 16px;
    font-size: 13px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--color-info);
}

.content-block p {
    margin-bottom: 12px;
}

.content-block ul {
    margin: 12px 0 0 24px;
}

/* ========================================
   TABLES
   ======================================== */
.academic-table {
    width: 100%;
    border-collapse: separate;
    border-spacing: 0;
    margin: 28px 0;
    font-size: 14px;
    border: 1px solid var(--border-light);
    border-radius: var(--radius-lg);
    overflow: hidden;
    box-shadow: var(--shadow-xs);
}

.academic-table th,
.academic-table td {
    padding: 14px 18px;
    text-align: left;
    vertical-align: top;
    border-bottom: 1px solid var(--border-light);
}

.academic-table th {
    background-color: var(--brand-primary);
    color: #ffffff;
    font-weight: 600;
    text-transform: uppercase;
    font-size: 11.5px;
    letter-spacing: 0.06em;
}

body:not(.dark-mode) .academic-table th {
    background-color: #1b2a3d;
}

.academic-table td {
    background-color: var(--bg-secondary);
}

.academic-table tr:nth-child(even) td {
    background-color: var(--bg-tertiary);
}

.academic-table tr:last-child td {
    border-bottom: none;
}

.academic-table td strong {
    color: var(--text-primary);
    font-weight: 600;
}

/* Compact Table Variant */
.academic-table.compact td,
.academic-table.compact th {
    padding: 10px 14px;
    font-size: 13px;
}

/* ========================================
   NAVIGATION CARDS
   ======================================== */
.nav-cards {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 20px;
    margin-top: 32px;
}

.nav-card {
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-lg);
    padding: 28px;
    text-decoration: none;
    color: var(--text-secondary);
    display: block;
    transition: box-shadow 0.2s ease, border-color 0.2s ease, transform 0.2s ease;
    box-shadow: var(--shadow-xs);
}

.nav-card:hover {
    border-color: var(--border-medium);
    box-shadow: var(--shadow-md);
    transform: translateY(-2px);
}

.nav-card h3 {
    font-size: 16px;
    font-weight: 700;
    margin-bottom: 8px;
    color: var(--text-primary);
}

.nav-card p {
    font-size: 14px;
    margin: 0;
    color: var(--text-muted);
    line-height: 1.6;
}

/* ========================================
   UNIT NAVIGATION
   ======================================== */
.unit-nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin: 48px 0;
    padding: 20px 0;
    border-top: 1px solid var(--border-light);
    border-bottom: 1px solid var(--border-light);
}

.unit-nav a {
    color: var(--text-primary);
    text-decoration: none;
    font-weight: 600;
    font-size: 14px;
    padding: 10px 24px;
    border: 1px solid var(--border-medium);
    border-radius: var(--radius-md);
    transition: all 0.2s ease;
}

.unit-nav a:hover {
    background-color: var(--text-primary);
    color: var(--bg-primary);
    border-color: var(--text-primary);
}

/* ========================================
   KEY POINTS BOX
   ======================================== */
.key-points {
    background-color: var(--bg-accent);
    border: 1px solid var(--border-light);
    border-left: 4px solid var(--color-info);
    border-radius: 0 var(--radius-lg) var(--radius-lg) 0;
    padding: 24px 28px;
    margin: 32px 0;
}

.key-points h4 {
    margin-top: 0;
    margin-bottom: 14px;
    font-size: 12px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--color-info);
}

.key-points ul {
    margin: 0 0 0 20px;
}

.key-points li {
    margin-bottom: 8px;
    line-height: 1.65;
}

/* ========================================
   DEFINITION BOX
   ======================================== */
.definition {
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-light);
    border-top: 3px solid var(--color-info);
    border-radius: var(--radius-lg);
    padding: 24px 28px;
    margin: 28px 0;
    box-shadow: var(--shadow-xs);
}

.definition strong {
    display: block;
    margin-bottom: 10px;
    font-size: 13px;
    font-weight: 700;
    color: var(--color-info);
    text-transform: uppercase;
    letter-spacing: 0.04em;
}

.definition p {
    margin: 0;
    line-height: 1.75;
    color: var(--text-secondary);
}

/* ========================================
   EXAM NOTES BOX
   ======================================== */
.exam-note {
    background-color: var(--color-warning-bg);
    border: 1px solid var(--color-warning-border);
    border-left: 4px solid var(--color-warning);
    border-radius: 0 var(--radius-lg) var(--radius-lg) 0;
    padding: 20px 24px;
    margin: 24px 0;
}

.exam-note h4 {
    margin: 0 0 10px 0;
    font-size: 12px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--color-warning);
}

.exam-note p,
.exam-note ul {
    margin: 0;
    font-size: 14px;
    line-height: 1.65;
}

.exam-note ul {
    margin-left: 20px;
    margin-top: 8px;
}

/* ========================================
   UNIT SUMMARY BOX
   ======================================== */
.unit-summary {
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-light);
    border-top: 3px solid var(--text-primary);
    border-radius: var(--radius-lg);
    padding: 32px;
    margin: 48px 0 32px 0;
    box-shadow: var(--shadow-sm);
}

.unit-summary h3 {
    margin: 0 0 20px 0;
    font-size: 14px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--text-primary);
    text-align: center;
    padding-bottom: 16px;
    border-bottom: 1px solid var(--border-light);
}

.unit-summary ul {
    margin: 0 0 0 24px;
}

.unit-summary li {
    margin-bottom: 10px;
    line-height: 1.65;
}

/* ========================================
   QUESTION SECTION
   ======================================== */
.question-section {
    margin: 32px 0;
}

.question-section h4 {
    margin-bottom: 20px;
    font-size: 17px;
    font-weight: 600;
}

.question-item {
    margin-bottom: 16px;
    padding: 20px 24px;
    border: 1px solid var(--border-light);
    border-radius: var(--radius-lg);
    background-color: var(--bg-secondary);
    box-shadow: var(--shadow-xs);
    transition: border-color 0.2s ease;
}

.question-item:hover {
    border-color: var(--border-medium);
}

.question-item p {
    margin: 0;
    line-height: 1.65;
}

.question-item .marks {
    font-weight: 700;
    color: #ffffff;
    background-color: var(--color-info);
    font-size: 11px;
    padding: 3px 10px;
    margin-left: 8px;
    border-radius: var(--radius-sm);
    display: inline-block;
    letter-spacing: 0.02em;
}

/* ========================================
   REVISION CHECKLIST
   ======================================== */
.checklist {
    list-style: none;
    margin-left: 0;
}

.checklist li {
    padding: 14px 0 14px 36px;
    border-bottom: 1px solid var(--border-light);
    position: relative;
    line-height: 1.6;
}

.checklist li:last-child {
    border-bottom: none;
}

.checklist li:before {
    content: "";
    position: absolute;
    left: 0;
    top: 16px;
    width: 16px;
    height: 16px;
    border: 2px solid var(--border-medium);
    border-radius: 3px;
    background-color: var(--bg-secondary);
}

/* ========================================
   SUMMARY BOX
   ======================================== */
.summary-box {
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-light);
    border-top: 3px solid var(--text-primary);
    border-radius: var(--radius-lg);
    padding: 28px 32px;
    margin: 32px 0;
    box-shadow: var(--shadow-sm);
}

.summary-box h4 {
    margin-top: 0;
    text-align: center;
    padding-bottom: 16px;
    margin-bottom: 16px;
    border-bottom: 1px solid var(--border-light);
    font-size: 13px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--text-primary);
}

.summary-box ul {
    margin: 0 0 0 24px;
}

.summary-box li {
    margin-bottom: 8px;
    line-height: 1.65;
}

/* ========================================
   SYLLABUS UNIT BLOCK
   ======================================== */
.syllabus-unit {
    margin-bottom: 24px;
    padding: 28px 32px;
    border: 1px solid var(--border-light);
    border-radius: var(--radius-lg);
    background-color: var(--bg-secondary);
    box-shadow: var(--shadow-xs);
}

.syllabus-unit h3 {
    margin-top: 0;
    padding-bottom: 16px;
    margin-bottom: 20px;
    border-bottom: 2px solid var(--text-primary);
    font-size: 18px;
    font-weight: 700;
    color: var(--text-primary);
}

.lecture-count {
    font-weight: 600;
    margin-top: 20px;
    text-align: right;
    font-size: 13px;
    color: var(--text-muted);
    padding-top: 16px;
    border-top: 1px solid var(--border-light);
}

/* ========================================
   ANSWER KEYWORDS BOX
   ======================================== */
.answer-keywords {
    background-color: var(--bg-accent);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-md);
    padding: 20px 24px;
    margin: 16px 0 24px 0;
}

.answer-keywords h5 {
    margin: 0 0 12px 0;
    font-size: 11px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--color-info);
}

.answer-keywords p {
    margin: 0;
    font-size: 14px;
    line-height: 1.65;
}

/* ========================================
   FULL ANSWER BOX
   ======================================== */
.full-answer {
    background-color: var(--answer-bg);
    border: 1px solid var(--answer-border);
    border-left: 4px solid var(--answer-accent);
    border-radius: 0 var(--radius-lg) var(--radius-lg) 0;
    padding: 24px 28px;
    margin: 16px 0 24px 0;
}

.full-answer h5 {
    margin: 0 0 16px 0;
    font-size: 12px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--answer-accent);
}

.full-answer p {
    margin: 0 0 14px 0;
    font-size: 14px;
    line-height: 1.8;
    text-align: justify;
}

.full-answer p:last-child {
    margin-bottom: 0;
}

.full-answer ul {
    margin: 10px 0 16px 24px;
    padding: 0;
}

.full-answer li {
    margin-bottom: 8px;
    font-size: 14px;
    line-height: 1.75;
}

.full-answer strong {
    color: var(--text-primary);
}

/* Comparison Table within Answers */
.full-answer .comparison-table,
.comparison-table {
    width: 100%;
    border-collapse: separate;
    border-spacing: 0;
    margin: 16px 0;
    font-size: 13px;
    border: 1px solid var(--border-light);
    border-radius: var(--radius-md);
    overflow: hidden;
}

.comparison-table th,
.comparison-table td {
    padding: 10px 14px;
    text-align: left;
    vertical-align: top;
    border-bottom: 1px solid var(--border-light);
}

.comparison-table th {
    background-color: #1b2a3d;
    color: #ffffff;
    font-weight: 600;
    font-size: 11px;
    letter-spacing: 0.06em;
    text-transform: uppercase;
}

.comparison-table td {
    background-color: var(--bg-secondary);
}

.comparison-table tr:nth-child(even) td {
    background-color: var(--bg-tertiary);
}

.comparison-table tr:last-child td {
    border-bottom: none;
}

/* ========================================
   TOPIC LIST
   ======================================== */
.topic-list {
    margin: 20px 0;
}

.topic-list li {
    padding: 12px 0;
    border-bottom: 1px solid var(--border-light);
    line-height: 1.65;
}

.topic-list li:last-child {
    border-bottom: none;
}

/* ========================================
   SUBSECTION STYLING
   ======================================== */
.subsection {
    margin: 32px 0;
    padding: 24px 28px;
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-lg);
}

.subsection h4 {
    margin-top: 0;
    margin-bottom: 16px;
    font-size: 16px;
    font-weight: 700;
    color: var(--text-primary);
}

.subsection p {
    margin-bottom: 12px;
}

/* ========================================
   IMPORTANT NOTE
   ======================================== */
.important-note {
    background-color: var(--color-warning-bg);
    border: 1px solid var(--color-warning-border);
    border-left: 4px solid var(--color-warning);
    border-radius: 0 var(--radius-lg) var(--radius-lg) 0;
    padding: 20px 24px;
    margin: 24px 0;
}

.important-note strong {
    display: block;
    margin-bottom: 8px;
    font-size: 12px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    color: var(--color-warning);
}

/* ========================================
   SECTION DIVIDER
   ======================================== */
.section-divider {
    border: none;
    border-top: 1px solid var(--border-light);
    margin: 48px 0;
}

/* ========================================
   COMPARISON LAYOUT
   ======================================== */
.comparison-row {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 20px;
    margin: 28px 0;
}

.comparison-item {
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-lg);
    padding: 24px;
    box-shadow: var(--shadow-xs);
}

.comparison-item h4 {
    margin: 0 0 16px 0;
    font-size: 14px;
    font-weight: 700;
    color: var(--text-primary);
    text-transform: uppercase;
    letter-spacing: 0.04em;
}

.comparison-item ul {
    margin: 0 0 0 20px;
}

.comparison-item li {
    margin-bottom: 8px;
    font-size: 14px;
}

/* ========================================
   GLOSSARY - SEARCH BAR
   ======================================== */
.glossary-search {
    max-width: 640px;
    margin: 0 auto 32px;
    padding: 0;
}

.glossary-search input {
    width: 100%;
    padding: 14px 20px;
    font-size: 15px;
    font-family: inherit;
    border: 1px solid var(--border-medium);
    border-radius: var(--radius-lg);
    background-color: var(--bg-secondary);
    color: var(--text-primary);
    box-shadow: var(--shadow-sm);
    transition: border-color 0.2s ease, box-shadow 0.2s ease;
    outline: none;
}

.glossary-search input::placeholder {
    color: var(--text-muted);
}

.glossary-search input:focus {
    border-color: var(--color-info);
    box-shadow: 0 0 0 3px rgba(61, 96, 152, 0.12);
}

/* ========================================
   GLOSSARY - ALPHABET NAVIGATION
   ======================================== */
.alphabet-nav {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 6px;
    margin: 0 0 40px;
    padding: 20px 24px;
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-xs);
}

.alphabet-nav a {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 36px;
    height: 36px;
    font-size: 13px;
    font-weight: 600;
    text-decoration: none;
    color: var(--text-secondary);
    background-color: var(--bg-tertiary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-sm);
    transition: all 0.15s ease;
}

.alphabet-nav a:hover {
    background-color: var(--text-primary);
    color: var(--bg-primary);
    border-color: var(--text-primary);
}

/* ========================================
   GLOSSARY - SECTIONS & TERMS
   ======================================== */
.glossary-section {
    margin: 0 0 48px;
}

.glossary-section h2 {
    font-size: 32px;
    font-weight: 800;
    color: var(--text-primary);
    padding-bottom: 12px;
    margin-bottom: 24px;
    border-bottom: 2px solid var(--text-primary);
    letter-spacing: -0.02em;
}

.glossary-term {
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-lg);
    padding: 28px 32px;
    margin-bottom: 16px;
    box-shadow: var(--shadow-xs);
    transition: box-shadow 0.2s ease, border-color 0.2s ease;
}

.glossary-term:hover {
    box-shadow: var(--shadow-md);
    border-color: var(--border-medium);
}

.glossary-term h3 {
    font-size: 18px;
    font-weight: 700;
    color: var(--text-primary);
    margin: 0 0 12px;
    line-height: 1.35;
}

.glossary-term p {
    margin: 0 0 12px;
    font-size: 14.5px;
    line-height: 1.75;
    color: var(--text-secondary);
}

.glossary-term p:last-child {
    margin-bottom: 0;
}

.glossary-term ul {
    margin: 8px 0 14px 24px;
}

.glossary-term li {
    margin-bottom: 6px;
    font-size: 14px;
    line-height: 1.7;
    color: var(--text-secondary);
}

.glossary-term strong {
    color: var(--text-primary);
    font-weight: 600;
}

.term-category {
    display: inline-block;
    padding: 3px 10px;
    background-color: var(--bg-tertiary);
    border: 1px solid var(--border-light);
    color: var(--text-muted);
    border-radius: var(--radius-sm);
    font-size: 11px;
    font-weight: 600;
    letter-spacing: 0.04em;
    text-transform: uppercase;
    margin-bottom: 12px;
}

/* ========================================
   FOOTER
   ======================================== */
footer {
    background-color: var(--text-primary);
    color: rgba(255, 255, 255, 0.75);
    text-align: center;
    padding: 36px 24px;
    margin-top: 0;
}

footer p {
    margin: 4px 0;
    font-size: 13px;
    line-height: 1.6;
}

/* ========================================
   PRINT STYLES
   ======================================== */
@media print {
    header, footer, .unit-nav, .nav-cards,
    .dark-mode-toggle, .back-to-top, .bookmark-panel,
    .highlight-toolbar, .alphabet-nav, .glossary-search {
        display: none;
    }

    body {
        font-size: 11pt;
        line-height: 1.5;
        color: #000000;
        background: #ffffff;
    }

    main {
        max-width: 100%;
        padding: 0;
    }

    .content-section {
        page-break-inside: avoid;
    }

    .key-points, .definition, .exam-note, .summary-box {
        break-inside: avoid;
    }

    .academic-table {
        font-size: 10pt;
    }

    .academic-table th {
        background-color: #e0e0e0 !important;
        color: #000000 !important;
        -webkit-print-color-adjust: exact;
        print-color-adjust: exact;
    }

    .glossary-term, .content-block, .question-item,
    .nav-card, .syllabus-unit {
        box-shadow: none;
        border-radius: 0;
    }
}

/* ========================================
   RESPONSIVE DESIGN
   ======================================== */
@media (max-width: 768px) {
    .nav-container {
        flex-direction: column;
        padding: 12px 16px;
    }

    .nav-brand {
        padding: 10px 0;
    }

    .nav-menu {
        flex-wrap: wrap;
        justify-content: center;
        gap: 0;
    }

    .nav-menu a {
        padding: 10px 14px;
        font-size: 13px;
    }

    main {
        padding: 32px 20px;
    }

    .hero {
        padding: 40px 0 32px;
    }

    .hero h1 {
        font-size: 28px;
    }

    .nav-cards {
        grid-template-columns: 1fr;
    }

    .unit-nav {
        flex-direction: column;
        gap: 12px;
        text-align: center;
    }

    .unit-nav a {
        display: block;
        text-align: center;
    }

    .academic-table {
        font-size: 12px;
    }

    .academic-table th,
    .academic-table td {
        padding: 10px 12px;
    }

    .unit-overview,
    .key-points,
    .definition,
    .exam-note,
    .summary-box,
    .syllabus-unit,
    .content-block,
    .glossary-term {
        padding: 20px;
    }

    .comparison-row {
        grid-template-columns: 1fr;
    }

    .topics-covered ul {
        flex-direction: column;
    }

    .alphabet-nav {
        gap: 4px;
        padding: 14px 12px;
    }

    .alphabet-nav a {
        width: 32px;
        height: 32px;
        font-size: 12px;
    }

    .glossary-section h2 {
        font-size: 26px;
    }

    .glossary-term h3 {
        font-size: 16px;
    }
}

@media (max-width: 480px) {
    .hero h1 {
        font-size: 24px;
        letter-spacing: -0.01em;
    }

    .content-section h2 {
        font-size: 20px;
    }

    .content-section h3 {
        font-size: 18px;
    }

    .academic-table {
        font-size: 11px;
    }

    .academic-table th,
    .academic-table td {
        padding: 8px 10px;
    }

    .alphabet-nav a {
        width: 28px;
        height: 28px;
        font-size: 11px;
    }
}

/* ========================================
   DARK MODE TOGGLE BUTTON
   ======================================== */
.dark-mode-toggle {
    position: fixed;
    top: 80px;
    right: 20px;
    width: 42px;
    height: 42px;
    border-radius: var(--radius-lg);
    border: 1px solid var(--border-medium);
    background-color: var(--bg-secondary);
    color: var(--text-primary);
    cursor: pointer;
    z-index: 999;
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: var(--shadow-sm);
    transition: all 0.2s ease;
}

.dark-mode-toggle svg {
    width: 20px;
    height: 20px;
    fill: none;
    stroke: currentColor;
    stroke-width: 2;
    stroke-linecap: round;
    stroke-linejoin: round;
}

.dark-mode-toggle:hover {
    background-color: var(--bg-tertiary);
    border-color: var(--border-dark);
    box-shadow: var(--shadow-md);
}

.dark-mode-toggle:active {
    transform: scale(0.95);
}

/* ========================================
   BACK TO TOP BUTTON
   ======================================== */
.back-to-top {
    position: fixed;
    bottom: 28px;
    right: 20px;
    width: 42px;
    height: 42px;
    border-radius: var(--radius-lg);
    border: 1px solid var(--border-medium);
    background-color: var(--bg-secondary);
    color: var(--text-primary);
    cursor: pointer;
    z-index: 998;
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 0;
    visibility: hidden;
    transform: translateY(10px);
    transition: all 0.25s ease;
    box-shadow: var(--shadow-sm);
}

.back-to-top svg {
    width: 20px;
    height: 20px;
    fill: none;
    stroke: currentColor;
    stroke-width: 2.5;
    stroke-linecap: round;
    stroke-linejoin: round;
}

.back-to-top.visible {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.back-to-top:hover {
    background-color: var(--text-primary);
    color: var(--bg-primary);
    border-color: var(--text-primary);
    box-shadow: var(--shadow-md);
}

/* ========================================
   BOOKMARK SYSTEM
   ======================================== */
.bookmark-btn {
    position: absolute;
    right: -5px;
    top: 50%;
    transform: translateY(-50%);
    background: none;
    border: none;
    cursor: pointer;
    opacity: 0.3;
    transition: opacity 0.2s ease, transform 0.2s ease;
    padding: 5px;
    color: var(--text-muted);
}

.bookmark-btn svg {
    width: 18px;
    height: 18px;
    fill: none;
    stroke: currentColor;
    stroke-width: 2;
    stroke-linecap: round;
    stroke-linejoin: round;
}

.bookmark-btn:hover {
    opacity: 1;
    color: var(--color-info);
    transform: translateY(-50%) scale(1.15);
}

.bookmark-btn.bookmarked {
    opacity: 1;
    color: var(--color-info);
}

.bookmark-btn.bookmarked svg {
    fill: var(--color-info);
}

/* Bookmark Panel */
.bookmark-panel {
    position: fixed;
    top: 140px;
    right: -320px;
    width: 300px;
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-medium);
    border-right: none;
    border-radius: var(--radius-lg) 0 0 var(--radius-lg);
    box-shadow: var(--shadow-lg);
    z-index: 997;
    transition: right 0.3s ease;
}

.bookmark-panel.open {
    right: 0;
}

.bookmark-panel-toggle {
    position: absolute;
    left: -45px;
    top: 0;
    width: 45px;
    height: 45px;
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-medium);
    border-right: none;
    border-radius: var(--radius-lg) 0 0 var(--radius-lg);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--text-primary);
}

.bookmark-panel-toggle svg {
    width: 20px;
    height: 20px;
    fill: none;
    stroke: currentColor;
    stroke-width: 2;
}

.bookmark-panel-content {
    padding: 20px;
    max-height: 400px;
    overflow-y: auto;
}

.bookmark-panel-content h4 {
    margin: 0 0 15px 0;
    font-size: 14px;
    font-weight: 700;
    color: var(--text-primary);
    padding-bottom: 10px;
    border-bottom: 1px solid var(--border-light);
}

.bookmark-item {
    display: block;
    padding: 10px 12px;
    margin-bottom: 6px;
    background-color: var(--bg-tertiary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-sm);
    text-decoration: none;
    color: var(--text-secondary);
    transition: background-color 0.15s ease, border-color 0.15s ease;
}

.bookmark-item:hover {
    background-color: var(--bg-accent);
    border-color: var(--border-medium);
}

.bookmark-title {
    display: block;
    font-size: 13px;
    font-weight: 600;
    margin-bottom: 2px;
}

.bookmark-page {
    display: block;
    font-size: 11px;
    color: var(--text-muted);
    text-transform: capitalize;
}

.no-bookmarks {
    font-size: 13px;
    color: var(--text-muted);
    font-style: italic;
}

.clear-bookmarks-btn {
    width: 100%;
    padding: 10px;
    margin-top: 15px;
    background-color: #b91c1c;
    color: white;
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 13px;
    font-weight: 500;
    transition: background-color 0.2s ease;
}

.clear-bookmarks-btn:hover {
    background-color: #991b1b;
}

/* ========================================
   HIGHLIGHT SYSTEM
   ======================================== */
.highlight-toolbar {
    position: absolute;
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-medium);
    border-radius: var(--radius-lg);
    padding: 8px 10px;
    display: flex;
    gap: 6px;
    box-shadow: var(--shadow-lg);
    z-index: 1001;
    opacity: 0;
    visibility: hidden;
    transform: translateY(-8px);
    transition: all 0.2s ease;
}

.highlight-toolbar.visible {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.highlight-toolbar button {
    background: none;
    border: 1px solid var(--border-light);
    cursor: pointer;
    padding: 5px;
    border-radius: var(--radius-sm);
    transition: background-color 0.15s ease;
    width: 28px;
    height: 28px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.highlight-toolbar button svg {
    width: 16px;
    height: 16px;
    fill: none;
    stroke: currentColor;
    stroke-width: 2;
}

.highlight-toolbar button:hover {
    background-color: var(--bg-tertiary);
}

/* User Highlights */
.user-highlight {
    border-radius: 2px;
    padding: 1px 2px;
}

.highlight-yellow {
    background-color: var(--highlight-yellow);
}

.highlight-green {
    background-color: var(--highlight-green);
}

.highlight-blue {
    background-color: var(--highlight-blue);
}

.highlight-note {
    background-color: var(--highlight-note);
    cursor: help;
    border-bottom: 2px dotted #e91e63;
}

/* ========================================
   TOAST NOTIFICATIONS
   ======================================== */
.toast {
    position: fixed;
    bottom: 90px;
    left: 50%;
    transform: translateX(-50%) translateY(10px);
    background-color: var(--text-primary);
    color: var(--bg-primary);
    padding: 12px 24px;
    border-radius: var(--radius-lg);
    font-size: 14px;
    font-weight: 500;
    z-index: 2000;
    opacity: 0;
    transition: all 0.25s ease;
    box-shadow: var(--shadow-lg);
}

.toast.show {
    opacity: 1;
    transform: translateX(-50%) translateY(0);
}

/* ========================================
   DARK MODE SPECIFIC OVERRIDES
   ======================================== */
body.dark-mode header {
    background-color: var(--bg-secondary);
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.4);
}

body.dark-mode .nav-brand {
    color: var(--text-primary);
}

body.dark-mode .nav-menu a {
    color: var(--text-muted);
}

body.dark-mode .nav-menu a:hover {
    color: var(--text-primary);
    background-color: rgba(255, 255, 255, 0.05);
}

body.dark-mode .nav-menu a.active {
    color: var(--text-primary);
    border-bottom-color: var(--brand-accent);
}

body.dark-mode .dropdown-menu {
    background-color: var(--bg-secondary);
    border-color: var(--border-medium);
}

body.dark-mode .dropdown-menu a {
    color: var(--text-secondary);
    border-color: var(--border-light);
}

body.dark-mode .dropdown-menu a:hover {
    background-color: var(--bg-tertiary);
    color: var(--text-primary);
}

/* Dark mode hero */
body.dark-mode .hero h1 {
    color: var(--text-primary);
}

/* Dark mode links */
body.dark-mode a {
    color: var(--brand-accent);
}

body.dark-mode a:hover {
    color: #8bbde8;
}

body.dark-mode .nav-menu a,
body.dark-mode .nav-brand {
    color: var(--text-secondary);
}

body.dark-mode .nav-menu a:hover {
    color: var(--text-primary);
}

/* Dark mode tables */
body.dark-mode .academic-table th {
    background-color: var(--brand-secondary);
}

body.dark-mode .academic-table td {
    background-color: var(--bg-secondary);
    border-color: var(--border-light);
}

body.dark-mode .academic-table tr:nth-child(even) td {
    background-color: var(--bg-tertiary);
}

body.dark-mode .comparison-table th {
    background-color: var(--brand-secondary);
}

body.dark-mode .comparison-table td {
    background-color: var(--bg-secondary);
    border-color: var(--border-light);
}

body.dark-mode .comparison-table tr:nth-child(even) td {
    background-color: var(--bg-tertiary);
}

/* Dark mode cards and boxes */
body.dark-mode .unit-overview {
    border-top-color: var(--brand-accent);
}

body.dark-mode .definition {
    border-top-color: var(--color-info);
}

body.dark-mode .key-points {
    border-left-color: var(--color-info);
}

body.dark-mode .exam-note {
    border-left-color: var(--color-warning);
}

body.dark-mode .unit-nav a {
    color: var(--text-secondary);
    border-color: var(--border-medium);
}

body.dark-mode .unit-nav a:hover {
    background-color: var(--text-primary);
    color: var(--bg-primary);
    border-color: var(--text-primary);
}

body.dark-mode .nav-card {
    background-color: var(--bg-secondary);
    border-color: var(--border-light);
}

body.dark-mode .nav-card:hover {
    border-color: var(--border-medium);
    background-color: var(--bg-tertiary);
}

body.dark-mode .topics-covered li {
    background-color: var(--bg-tertiary);
    border-color: var(--border-light);
}

body.dark-mode footer {
    background-color: var(--bg-secondary);
    border-top: 1px solid var(--border-light);
}

body.dark-mode .marks {
    background-color: var(--brand-secondary);
}

/* Dark mode glossary */
body.dark-mode .alphabet-nav a {
    background-color: var(--bg-tertiary);
    border-color: var(--border-light);
    color: var(--text-secondary);
}

body.dark-mode .alphabet-nav a:hover {
    background-color: var(--text-primary);
    color: var(--bg-primary);
    border-color: var(--text-primary);
}

body.dark-mode .glossary-search input {
    background-color: var(--bg-tertiary);
    border-color: var(--border-medium);
    color: var(--text-primary);
}

body.dark-mode .glossary-search input:focus {
    border-color: var(--brand-accent);
    box-shadow: 0 0 0 3px rgba(106, 159, 216, 0.15);
}

body.dark-mode .term-category {
    background-color: var(--bg-tertiary);
    border-color: var(--border-medium);
    color: var(--text-muted);
}

/* ========================================
   ACCESSIBILITY IMPROVEMENTS
   ======================================== */
:focus-visible {
    outline: 2px solid var(--color-info);
    outline-offset: 2px;
}

/* Skip link for keyboard navigation */
.skip-link {
    position: absolute;
    top: -100px;
    left: 0;
    background-color: var(--text-primary);
    color: white;
    padding: 12px 24px;
    z-index: 10000;
    text-decoration: none;
    font-weight: 600;
}

.skip-link:focus {
    top: 0;
}

/* ========================================
   RESPONSIVE ADJUSTMENTS FOR FEATURES
   ======================================== */
@media (max-width: 768px) {
    .dark-mode-toggle {
        top: auto;
        bottom: 84px;
        right: 16px;
        width: 42px;
        height: 42px;
    }

    .back-to-top {
        right: 16px;
        bottom: 24px;
        width: 42px;
        height: 42px;
    }

    .bookmark-panel {
        width: 260px;
        right: -280px;
    }

    .bookmark-btn {
        right: -2px;
    }

    .highlight-toolbar {
        left: 50% !important;
        transform: translateX(-50%) translateY(-8px);
    }

    .highlight-toolbar.visible {
        transform: translateX(-50%) translateY(0);
    }
}

/* Unit In-Page TOC Navigation */
.unit-toc {
    background: var(--card-bg, #f8f9fa);
    border: 1px solid var(--border-color, #dee2e6);
    border-left: 4px solid var(--primary-color, #2196F3);
    border-radius: 8px;
    padding: 1.5rem;
    margin: 1.5rem 0;
}

.unit-toc h3 {
    margin: 0 0 1rem 0;
    font-size: 1rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--primary-color, #2196F3);
}

.unit-toc ul {
    list-style: none;
    padding: 0;
    margin: 0;
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 0.4rem;
}

.unit-toc li a {
    display: block;
    padding: 0.3rem 0.5rem;
    border-radius: 4px;
    color: var(--text-color, #333);
    text-decoration: none;
    font-size: 0.9rem;
    transition: background 0.2s, color 0.2s;
}

.unit-toc li a:hover {
    background: var(--primary-color, #2196F3);
    color: #fff;
}

/* ========================================
   SIDEBAR NAVIGATION
   ======================================== */
.sidebar-nav {
    position: fixed;
    left: 0;
    top: 0;
    width: 250px;
    height: 100vh;
    padding-top: 64px;
    overflow-y: auto;
    background: var(--bg-secondary);
    border-right: 1px solid var(--border-light);
    z-index: 900;
    transition: transform 0.3s ease;
}

.sidebar-nav .sidebar-header {
    padding: 16px 16px 8px;
    font-size: 11px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--text-muted);
}

.sidebar-nav ul {
    list-style: none;
    padding: 0;
    margin: 0;
}

.sidebar-nav li a {
    display: block;
    padding: 7px 16px 7px 19px;
    font-size: 13px;
    color: var(--text-muted);
    text-decoration: none;
    border-left: 3px solid transparent;
    transition: all 0.15s ease;
    line-height: 1.45;
}

.sidebar-nav li a:hover {
    color: var(--text-primary);
    background: var(--bg-tertiary);
}

.sidebar-nav li a.active {
    color: var(--brand-accent);
    border-left-color: var(--brand-accent);
    background: var(--bg-accent);
    font-weight: 600;
}

.sidebar-nav::-webkit-scrollbar {
    width: 4px;
}

.sidebar-nav::-webkit-scrollbar-track {
    background: transparent;
}

.sidebar-nav::-webkit-scrollbar-thumb {
    background: var(--border-medium);
    border-radius: 4px;
}

/* Adjust main when sidebar is present */
body.has-sidebar main {
    margin-left: 250px;
    max-width: 880px;
}

/* Mobile sidebar toggle button */
.sidebar-toggle {
    display: none;
    position: fixed;
    left: 12px;
    bottom: 80px;
    width: 44px;
    height: 44px;
    border-radius: 50%;
    background: var(--brand-primary);
    color: #fff;
    border: none;
    cursor: pointer;
    z-index: 1001;
    box-shadow: var(--shadow-md);
    align-items: center;
    justify-content: center;
}

.sidebar-toggle svg {
    width: 20px;
    height: 20px;
    stroke: currentColor;
    fill: none;
    stroke-linecap: round;
}

body.dark-mode .sidebar-toggle {
    background: var(--brand-accent);
}

/* Responsive: hide sidebar on smaller screens, show toggle */
@media (max-width: 1200px) {
    .sidebar-nav {
        transform: translateX(-100%);
        box-shadow: none;
    }

    .sidebar-nav.mobile-open {
        transform: translateX(0);
        box-shadow: var(--shadow-lg);
    }

    body.has-sidebar main {
        margin-left: 0;
        max-width: 880px;
    }

    .sidebar-toggle {
        display: flex;
    }
}

/* Print: hide sidebar */
@media print {
    .sidebar-nav,
    .sidebar-toggle {
        display: none !important;
    }

    body.has-sidebar main {
        margin-left: 0;
    }
}

/* Sidebar overlay for mobile */
.sidebar-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.4);
    z-index: 899;
}

.sidebar-overlay.visible {
    display: block;
}