/* ===========================
   Programming Fundamentals: Three Language Approach
   Main CSS — based on course_template
   Mobile-first, Responsive, Accessible
   =========================== */

/* ===========================
   CSS Reset
   =========================== */
html, body, div, span, applet, object, iframe,
h1, h2, h3, h4, h5, h6, p, blockquote, pre,
a, abbr, acronym, address, big, cite, code,
del, dfn, em, img, ins, kbd, q, s, samp,
small, strike, strong, sub, sup, tt, var,
b, u, i, center, dl, dt, dd, ol, ul, li,
fieldset, form, label, legend, table, caption, tbody, tfoot, thead, tr, th, td,
article, aside, canvas, details, embed,
figure, figcaption, footer, header, hgroup,
menu, nav, output, ruby, section, summary,
time, mark, audio, video {
    margin: 0;
    padding: 0;
    border: 0;
    font-size: 100%;
    font: inherit;
    vertical-align: baseline;
}

article, aside, details, figcaption, figure,
footer, header, hgroup, menu, nav, section {
    display: block;
}

body { line-height: 1; }
ol, ul { list-style: none; }
blockquote, q { quotes: none; }
blockquote:before, blockquote:after, q:before, q:after { content: ''; content: none; }
table { border-collapse: collapse; border-spacing: 0; }

/* ===========================
   CSS Variables — Light (default)
   =========================== */
:root {
    /* Surface colors */
    --bg-color: #f8fafc;
    --card-bg: #ffffff;
    --nav-bg: #ffffff;
    --text-color: #1e293b;
    --text-light: #64748b;
    --border-color: #e2e8f0;

    /* Primary accent */
    --primary-color: #3b82f6;
    --primary-hover: #2563eb;
    --primary-light: rgba(59, 130, 246, 0.08);
    --primary-gradient: linear-gradient(135deg, #3b82f6 0%, #6366f1 100%);

    /* Language accent colors */
    --python-color: #3776ab;
    --python-bg: rgba(55, 118, 171, 0.08);
    --javascript-color: #f7df1e;
    --javascript-bg: rgba(247, 223, 30, 0.08);
    --csharp-color: #68217a;
    --csharp-bg: rgba(104, 33, 122, 0.08);

    /* Code */
    --code-bg: #f1f5f9;
    --code-color: #334155;

    /* Prism tokens (light) */
    --tok-comment: #6a737d;
    --tok-string:  #50a14f;
    --tok-keyword: #4078f2;
    --tok-function:#c18401;
    --tok-number:  #e45649;
    --tok-operator:#a626a4;

    /* Semantic cards */
    --success-bg: #f0fdf4;
    --success-border: #22c55e;
    --warning-bg: #fffbeb;
    --warning-border: #f59e0b;
    --info-bg: #eff6ff;
    --info-border: #3b82f6;
    --danger-bg: #fef2f2;
    --danger-border: #ef4444;

    /* Shadows */
    --shadow-sm: 0 1px 2px rgba(0,0,0,0.05);
    --shadow-md: 0 4px 6px -1px rgba(0,0,0,0.07), 0 2px 4px -2px rgba(0,0,0,0.05);
    --shadow-lg: 0 10px 15px -3px rgba(0,0,0,0.08), 0 4px 6px -4px rgba(0,0,0,0.04);

    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-xxl: 3rem;

    /* Typography */
    --font-family-base: 'Segoe UI', system-ui, -apple-system, sans-serif;
    --font-family-mono: 'Cascadia Code', 'Fira Code', 'Consolas', 'Monaco', monospace;
    --line-height-base: 1.7;
    --line-height-heading: 1.25;

    /* Misc */
    --radius-sm: 6px;
    --radius-md: 10px;
    --radius-lg: 16px;

    color-scheme: light dark;
}

/* ===========================
   Dark theme variables
   =========================== */
:root[data-theme="dark"] {
    --bg-color: #0f172a;
    --card-bg: #1e293b;
    --nav-bg: #1e293b;
    --text-color: #e2e8f0;
    --text-light: #94a3b8;
    --border-color: #334155;

    --primary-light: rgba(59, 130, 246, 0.15);

    --python-bg: rgba(55, 118, 171, 0.15);
    --javascript-bg: rgba(247, 223, 30, 0.12);
    --csharp-bg: rgba(104, 33, 122, 0.15);

    --code-bg: #1e293b;
    --code-color: #e2e8f0;

    --tok-comment: #6b7280;
    --tok-string:  #86efac;
    --tok-keyword: #93c5fd;
    --tok-function:#fcd34d;
    --tok-number:  #fca5a5;
    --tok-operator:#c4b5fd;

    --success-bg: rgba(34, 197, 94, 0.1);
    --success-border: #22c55e;
    --warning-bg: rgba(245, 158, 11, 0.1);
    --warning-border: #f59e0b;
    --info-bg: rgba(59, 130, 246, 0.1);
    --info-border: #3b82f6;
    --danger-bg: rgba(239, 68, 68, 0.1);
    --danger-border: #ef4444;

    --shadow-sm: 0 1px 2px rgba(0,0,0,0.3);
    --shadow-md: 0 4px 6px -1px rgba(0,0,0,0.4), 0 2px 4px -2px rgba(0,0,0,0.3);
    --shadow-lg: 0 10px 15px -3px rgba(0,0,0,0.5), 0 4px 6px -4px rgba(0,0,0,0.3);
}

/* OS-level dark preference (no explicit toggle yet) */
@media (prefers-color-scheme: dark) {
    :root:not([data-theme="light"]) {
        --bg-color: #0f172a;
        --card-bg: #1e293b;
        --nav-bg: #1e293b;
        --text-color: #e2e8f0;
        --text-light: #94a3b8;
        --border-color: #334155;
        --primary-light: rgba(59, 130, 246, 0.15);
        --python-bg: rgba(55, 118, 171, 0.15);
        --javascript-bg: rgba(247, 223, 30, 0.12);
        --csharp-bg: rgba(104, 33, 122, 0.15);
        --code-bg: #1e293b;
        --code-color: #e2e8f0;
        --tok-comment: #6b7280;
        --tok-string:  #86efac;
        --tok-keyword: #93c5fd;
        --tok-function:#fcd34d;
        --tok-number:  #fca5a5;
        --tok-operator:#c4b5fd;
        --success-bg: rgba(34, 197, 94, 0.1);
        --success-border: #22c55e;
        --warning-bg: rgba(245, 158, 11, 0.1);
        --warning-border: #f59e0b;
        --info-bg: rgba(59, 130, 246, 0.1);
        --info-border: #3b82f6;
        --danger-bg: rgba(239, 68, 68, 0.1);
        --danger-border: #ef4444;
        --shadow-sm: 0 1px 2px rgba(0,0,0,0.3);
        --shadow-md: 0 4px 6px -1px rgba(0,0,0,0.4), 0 2px 4px -2px rgba(0,0,0,0.3);
        --shadow-lg: 0 10px 15px -3px rgba(0,0,0,0.5), 0 4px 6px -4px rgba(0,0,0,0.3);
    }
}

/* Force light when explicitly set */
:root[data-theme="light"] {
    --bg-color: #f8fafc;
    --card-bg: #ffffff;
    --nav-bg: #ffffff;
    --text-color: #1e293b;
    --text-light: #64748b;
    --border-color: #e2e8f0;
    --primary-light: rgba(59, 130, 246, 0.08);
    --python-bg: rgba(55, 118, 171, 0.08);
    --javascript-bg: rgba(247, 223, 30, 0.08);
    --csharp-bg: rgba(104, 33, 122, 0.08);
    --code-bg: #f1f5f9;
    --code-color: #334155;
    --tok-comment: #6a737d;
    --tok-string:  #50a14f;
    --tok-keyword: #4078f2;
    --tok-function:#c18401;
    --tok-number:  #e45649;
    --tok-operator:#a626a4;
    --success-bg: #f0fdf4;
    --success-border: #22c55e;
    --warning-bg: #fffbeb;
    --warning-border: #f59e0b;
    --info-bg: #eff6ff;
    --info-border: #3b82f6;
    --danger-bg: #fef2f2;
    --danger-border: #ef4444;
    --shadow-sm: 0 1px 2px rgba(0,0,0,0.05);
    --shadow-md: 0 4px 6px -1px rgba(0,0,0,0.07), 0 2px 4px -2px rgba(0,0,0,0.05);
    --shadow-lg: 0 10px 15px -3px rgba(0,0,0,0.08), 0 4px 6px -4px rgba(0,0,0,0.04);
}

/* ===========================
   Base Styles — Mobile First
   =========================== */

body {
    font-family: var(--font-family-base);
    font-size: 16px;
    line-height: var(--line-height-base);
    color: var(--text-color);
    background-color: var(--bg-color);
    margin: 0;
    padding: var(--spacing-md);
    padding-bottom: calc(var(--spacing-md) + env(safe-area-inset-bottom));
    transition: background-color 0.3s ease, color 0.3s ease;
}

p, li, figcaption, blockquote { overflow-wrap: anywhere; }

.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

/* ===========================
   Typography
   =========================== */

h1, h2, h3, h4, h5, h6 {
    font-weight: 700;
    line-height: var(--line-height-heading);
    margin-top: var(--spacing-xl);
    margin-bottom: var(--spacing-md);
    color: var(--text-color);
}

h1 {
    font-size: 2rem;
    text-align: center;
    padding: var(--spacing-lg) var(--spacing-md);
    background: var(--primary-gradient);
    color: #fff;
    margin: 0 0 var(--spacing-xl) 0;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
}

h2 {
    font-size: 1.6rem;
    border-bottom: 3px solid var(--primary-color);
    padding-bottom: var(--spacing-sm);
}

h3 { font-size: 1.35rem; }
h4 { font-size: 1.15rem; }
h5 { font-size: 1.05rem; }
h6 { font-size: 1rem; }

p { margin-bottom: var(--spacing-md); }
strong, b { font-weight: 700; }
em, i { font-style: italic; }
small { font-size: 0.875rem; }

.lead {
    font-size: 1.15rem;
    color: var(--text-light);
    max-width: 700px;
    margin: 0 auto var(--spacing-lg);
    text-align: center;
}

/* Links */
a {
    color: var(--primary-color);
    text-decoration: underline;
    text-underline-offset: 3px;
    text-decoration-thickness: 1.5px;
    transition: color 0.2s, text-decoration-thickness 0.2s;
}
a:hover {
    color: var(--primary-hover);
    text-decoration-thickness: 2.5px;
}

a:focus-visible,
button:focus-visible,
[role="button"]:focus-visible,
input:focus-visible,
select:focus-visible,
textarea:focus-visible {
    outline: 3px solid var(--primary-color);
    outline-offset: 2px;
}

/* Lists */
ul, ol { margin: var(--spacing-md) 0; padding-left: var(--spacing-xl); }
ul { list-style-type: disc; }
ol { list-style-type: decimal; }
li { margin-bottom: var(--spacing-sm); }
ul ul, ol ol, ul ol, ol ul { margin-top: var(--spacing-sm); margin-bottom: var(--spacing-sm); }

/* ===========================
   Code and Pre
   =========================== */

code, pre {
    font-family: var(--font-family-mono);
    background-color: var(--code-bg);
    color: var(--code-color);
    border-radius: var(--radius-sm);
}

code {
    padding: 0.15em 0.4em;
    font-size: 0.88em;
}

pre {
    padding: var(--spacing-md);
    overflow-x: auto;
    line-height: 1.55;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    margin: var(--spacing-md) 0;
    white-space: pre;
}

pre code {
    padding: 0;
    background: transparent;
    font-size: 0.875rem;
}

/* Prism-compatible tokens */
.token.comment  { color: var(--tok-comment);  font-style: italic; }
.token.string   { color: var(--tok-string); }
.token.keyword  { color: var(--tok-keyword); }
.token.function { color: var(--tok-function); }
.token.number   { color: var(--tok-number); }
.token.operator { color: var(--tok-operator); }

/* ===========================
   Tables
   =========================== */

.table-wrap { overflow-x: auto; }

table {
    width: 100%;
    margin: var(--spacing-md) 0;
    border-collapse: collapse;
}

th, td {
    padding: var(--spacing-sm) var(--spacing-md);
    text-align: left;
    border: 1px solid var(--border-color);
}

th {
    background-color: var(--primary-color);
    color: #fff;
    font-weight: 700;
}

tr:nth-child(even) { background-color: var(--primary-light); }

/* ===========================
   Blockquotes
   =========================== */

blockquote {
    margin: var(--spacing-lg) 0;
    padding: var(--spacing-md) var(--spacing-lg);
    background-color: var(--primary-light);
    border-left: 4px solid var(--primary-color);
    border-radius: 0 var(--radius-md) var(--radius-md) 0;
    font-style: italic;
    color: var(--text-color);
}

/* ===========================
   Images and Media
   =========================== */

img {
    max-width: 100%;
    height: auto;
    display: block;
    margin: var(--spacing-md) auto;
    border-radius: var(--radius-md);
}

figure { margin: var(--spacing-lg) 0; text-align: center; }
figcaption { margin-top: var(--spacing-sm); font-size: 0.9rem; color: var(--text-light); }

/* ===========================
   Navigation
   =========================== */

nav:first-of-type,
nav.main-nav {
    background-color: var(--nav-bg);
    border-bottom: 1px solid var(--border-color);
    padding: calc(var(--spacing-sm) + env(safe-area-inset-top)) var(--spacing-md) var(--spacing-sm);
    position: sticky;
    top: 0;
    z-index: 200;
    box-shadow: var(--shadow-sm);
    transition: background-color 0.3s ease;
}

.nav-container {
    max-width: 1100px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
    position: relative;
}

.nav-logo {
    font-size: 1.15rem;
    font-weight: 700;
    color: var(--primary-color);
    text-decoration: none;
    white-space: nowrap;
}

.nav-links {
    display: flex;
    gap: var(--spacing-md);
    align-items: center;
    list-style: none;
    margin: 0;
    padding: 0;
}

.nav-links a {
    text-decoration: none;
    color: var(--text-color);
    font-weight: 500;
    font-size: 0.92rem;
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: var(--radius-sm);
    transition: color 0.2s, background-color 0.2s;
}
.nav-links a:hover {
    color: var(--primary-color);
    background-color: var(--primary-light);
}

.nav-divider {
    width: 1px;
    height: 1.2rem;
    background-color: var(--border-color);
    flex-shrink: 0;
}

/* Theme toggle button in nav */
#theme-toggle {
    background: var(--primary-light);
    border: 1px solid var(--border-color);
    border-radius: 50%;
    width: 36px;
    height: 36px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    font-size: 1.1rem;
    padding: 0;
    transition: background-color 0.2s, transform 0.2s;
}
#theme-toggle:hover {
    transform: scale(1.1);
    background-color: var(--primary-color);
}

/* Mobile menu toggle */
.mobile-menu-toggle {
    display: none;
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    color: var(--primary-color);
    padding: var(--spacing-xs);
}

/* ===========================
   Cards
   =========================== */

.card {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: var(--spacing-lg);
    margin: var(--spacing-md) 0;
    box-shadow: var(--shadow-sm);
    transition: box-shadow 0.3s ease, background-color 0.3s ease;
}
.card:hover { box-shadow: var(--shadow-md); }

.lesson-card { border-left: 4px solid var(--primary-color); }

/* Semantic card variants */
.card-success {
    background: var(--success-bg);
    border-left: 4px solid var(--success-border);
}
.card-warning {
    background: var(--warning-bg);
    border-left: 4px solid var(--warning-border);
}
.card-info {
    background: var(--info-bg);
    border-left: 4px solid var(--info-border);
}
.card-danger {
    background: var(--danger-bg);
    border-left: 4px solid var(--danger-border);
}
.card-accent {
    background: var(--primary-gradient);
    color: #fff;
    border: none;
}
.card-accent h3,
.card-accent h4,
.card-accent p { color: #fff; }

.card-output {
    background: var(--code-bg);
    border-left: 4px solid var(--success-border);
}

.exercise-card {
    background: var(--primary-gradient);
    color: #fff;
    border: none;
}
.exercise-card h3 { color: #fff; }

/* ===========================
   Buttons
   =========================== */

.button, button {
    display: inline-flex;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-sm) var(--spacing-lg);
    background-color: var(--primary-color);
    color: #fff;
    border: none;
    border-radius: var(--radius-sm);
    font-size: 0.95rem;
    font-weight: 600;
    text-decoration: none;
    cursor: pointer;
    transition: background-color 0.2s, transform 0.1s, box-shadow 0.2s;
}
.button:hover, button:hover {
    background-color: var(--primary-hover);
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}
.button:active, button:active { transform: translateY(0); }

.button-secondary {
    background-color: transparent;
    color: var(--primary-color);
    border: 2px solid var(--primary-color);
}
.button-secondary:hover {
    background-color: var(--primary-color);
    color: #fff;
}

/* ===========================
   Forms
   =========================== */

input, textarea, select {
    width: 100%;
    padding: var(--spacing-sm) var(--spacing-md);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    font-size: 1rem;
    font-family: inherit;
    transition: border-color 0.2s, box-shadow 0.2s;
    background: var(--card-bg);
    color: var(--text-color);
}
input:focus, textarea:focus, select:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.15);
}

label { display: block; margin-bottom: var(--spacing-xs); font-weight: 600; }

/* ===========================
   Utility Classes
   =========================== */

.text-center { text-align: center; }
.text-left { text-align: left; }
.text-right { text-align: right; }
.mt-0 { margin-top: 0; }
.mt-1 { margin-top: var(--spacing-sm); }
.mt-2 { margin-top: var(--spacing-md); }
.mt-3 { margin-top: var(--spacing-lg); }
.mt-4 { margin-top: var(--spacing-xl); }
.mb-0 { margin-bottom: 0; }
.mb-1 { margin-bottom: var(--spacing-sm); }
.mb-2 { margin-bottom: var(--spacing-md); }
.mb-3 { margin-bottom: var(--spacing-lg); }
.mb-4 { margin-bottom: var(--spacing-xl); }
.hidden { display: none; }
.block { display: block; }
.inline-block { display: inline-block; }
.flex { display: flex; }
.grid { display: grid; }

/* Screen reader only */
.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

/* ===========================
   Progress Indicator
   =========================== */

.progress-indicator {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 3px;
    background: var(--border-color);
    z-index: 1000;
}
.progress-bar {
    height: 100%;
    background: var(--primary-gradient);
    width: 0;
    transition: width 0.3s ease;
}

/* Skip to main content */
.skip-to-main {
    position: absolute;
    left: -10000px;
    top: 30px;
    z-index: 999;
    padding: var(--spacing-sm) var(--spacing-md);
    background: var(--primary-color);
    color: #fff;
    text-decoration: none;
    border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}
.skip-to-main:focus { left: 0; }

/* ===========================
   Lesson Navigation (prev/next)
   =========================== */

.lesson-nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin: var(--spacing-xxl) 0;
    padding: var(--spacing-lg);
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    flex-wrap: wrap;
    gap: var(--spacing-md);
    transition: background-color 0.3s ease;
}

.lesson-nav a {
    display: inline-flex;
    align-items: center;
    padding: var(--spacing-sm) var(--spacing-lg);
    background: var(--primary-color);
    color: #fff;
    text-decoration: none;
    border-radius: var(--radius-sm);
    transition: background-color 0.3s;
    font-weight: 600;
}
.lesson-nav a:hover { background: var(--primary-hover); }

.lesson-nav .home-link {
    background: transparent;
    color: var(--primary-color);
    border: 2px solid var(--primary-color);
}
.lesson-nav .home-link:hover {
    background: var(--primary-color);
    color: #fff;
}

/* ===========================
   Breadcrumb Navigation
   =========================== */

.breadcrumb {
    padding: var(--spacing-sm) var(--spacing-md);
    font-size: 0.88rem;
    background: transparent;
    border: none;
    box-shadow: none;
    position: static;
}

.breadcrumb ul {
    display: flex;
    list-style: none;
    padding: 0;
    margin: 0;
    flex-wrap: wrap;
    max-width: 1100px;
    margin: 0 auto;
}

.breadcrumb li::after {
    content: "›";
    margin: 0 var(--spacing-sm);
    color: var(--text-light);
}
.breadcrumb li:last-child::after { content: ""; }
.breadcrumb a { color: var(--primary-color); text-decoration: none; }
.breadcrumb [aria-current="page"] { color: var(--text-light); font-weight: 500; }

/* ===========================
   Sticky Table of Contents
   =========================== */

.toc-card {
    position: sticky;
    top: 70px;
    z-index: 100;
    background: var(--card-bg);
    box-shadow: var(--shadow-md);
    margin-bottom: var(--spacing-xl);
    transition: background-color 0.3s ease;
}
.toc-card summary {
    cursor: pointer;
    font-weight: 700;
    padding: var(--spacing-sm) var(--spacing-md);
    user-select: none;
}
.toc-card nav {
    padding: 0 var(--spacing-md) var(--spacing-md);
}

.toc-link {
    color: var(--text-color);
    text-decoration: none;
    transition: color 0.2s;
}
.toc-link:hover { color: var(--primary-color); }
.toc-link.active {
    color: var(--primary-color);
    font-weight: 600;
}

/* ===========================
   Quiz Styles
   =========================== */

.quiz-container { padding: var(--spacing-lg); }

.quiz-option {
    display: block;
    width: 100%;
    text-align: left;
    padding: var(--spacing-sm) var(--spacing-md);
    margin: var(--spacing-sm) 0;
    background: var(--card-bg);
    color: var(--text-color);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 0.95rem;
    transition: border-color 0.2s, background-color 0.2s;
}
.quiz-option:hover {
    border-color: var(--primary-color);
    background-color: var(--primary-light);
    transform: none;
    box-shadow: none;
}
.quiz-option.correct {
    border-color: var(--success-border);
    background-color: var(--success-bg);
}
.quiz-option.incorrect {
    border-color: var(--danger-border);
    background-color: var(--danger-bg);
}

.quiz-feedback {
    padding: var(--spacing-sm) var(--spacing-md);
    margin-top: var(--spacing-sm);
    border-radius: var(--radius-sm);
    font-weight: 500;
}
.quiz-feedback.correct { color: var(--success-border); }
.quiz-feedback.incorrect { color: var(--danger-border); }

/* ===========================
   Footer
   =========================== */

.site-footer {
    text-align: center;
    padding: var(--spacing-xl) var(--spacing-md);
    margin-top: var(--spacing-xxl);
    border-top: 1px solid var(--border-color);
    color: var(--text-light);
    font-size: 0.9rem;
}
.site-footer a { color: var(--primary-color); }
.footer-links {
    display: flex;
    justify-content: center;
    gap: var(--spacing-md);
    flex-wrap: wrap;
    margin-top: var(--spacing-sm);
}

/* ===========================
   SVG / Canvas / Mermaid Dark Mode
   =========================== */

:root[data-theme="dark"] .diagram-auto-invert svg,
:root[data-theme="dark"] .svg-auto-invert {
    filter: invert(0.88) hue-rotate(180deg);
}

:root[data-theme="dark"] canvas.auto-invert {
    filter: invert(0.88) hue-rotate(180deg);
}

.mermaid {
    text-align: center;
    margin: var(--spacing-lg) 0;
}

svg text { fill: var(--text-color); }
svg .svg-bg { fill: var(--card-bg); }

/* ===========================
   Search Results (dark-aware)
   =========================== */

#search-results {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    max-height: 300px;
    overflow-y: auto;
    z-index: 1000;
    box-shadow: var(--shadow-lg);
}

.search-result-item {
    padding: var(--spacing-sm) var(--spacing-md);
    cursor: pointer;
    border-bottom: 1px solid var(--border-color);
    transition: background-color 0.15s;
}
.search-result-item:hover { background-color: var(--primary-light); }

.highlight {
    animation: highlight-flash 2s ease;
}
@keyframes highlight-flash {
    0%, 100% { background-color: transparent; }
    30% { background-color: var(--warning-bg); }
}

/* ===========================
   Keyboard Shortcuts Modal
   =========================== */

.shortcuts-modal {
    position: fixed;
    inset: 0;
    background: rgba(0,0,0,0.5);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 9999;
}
.shortcuts-content {
    background: var(--card-bg);
    color: var(--text-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    max-width: 400px;
    width: 90%;
    box-shadow: var(--shadow-lg);
    position: relative;
}
.shortcuts-content .close-modal {
    position: absolute;
    top: var(--spacing-sm);
    right: var(--spacing-sm);
    background: transparent;
    color: var(--text-light);
    border: none;
    font-size: 1.5rem;
    padding: var(--spacing-xs);
    box-shadow: none;
}
.shortcuts-content .close-modal:hover {
    color: var(--text-color);
    transform: none;
    box-shadow: none;
}
.shortcuts-content dl {
    display: grid;
    grid-template-columns: auto 1fr;
    gap: var(--spacing-sm) var(--spacing-md);
    margin-top: var(--spacing-md);
}
.shortcuts-content dt {
    font-family: var(--font-family-mono);
    background: var(--code-bg);
    padding: 2px 8px;
    border-radius: 4px;
    font-size: 0.85rem;
    text-align: center;
}
.shortcuts-content dd { margin: 0; }

/* ===========================
   Progress bar (index page)
   =========================== */

.progress-bar-container {
    width: 100%;
    height: 8px;
    background: var(--border-color);
    border-radius: 4px;
    overflow: hidden;
    margin: var(--spacing-sm) 0;
}
.progress-bar-container .progress-bar {
    height: 100%;
    background: var(--primary-gradient);
    border-radius: 4px;
    transition: width 0.5s ease;
}

/* Lesson link visited checkmark */
.lesson-link { text-decoration: none; }
.lesson-link.visited { opacity: 0.8; }
.checkmark {
    color: var(--success-border);
    margin-left: var(--spacing-sm);
    font-weight: 700;
}

/* ===========================
   CODE TABS — Three-Language Comparison
   =========================== */

.code-tabs {
    margin: var(--spacing-lg) 0;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    overflow: hidden;
    background: var(--card-bg);
    box-shadow: var(--shadow-sm);
}

/* Tab bar */
.tab-bar {
    display: flex;
    align-items: center;
    gap: 0;
    background: var(--code-bg);
    border-bottom: 2px solid var(--border-color);
    padding: 0;
    overflow-x: auto;
    flex-wrap: nowrap;
}

.tab-bar-title {
    padding: var(--spacing-sm) var(--spacing-md);
    font-weight: 700;
    font-size: 0.85rem;
    color: var(--text-light);
    white-space: nowrap;
    border-right: 1px solid var(--border-color);
    flex-shrink: 0;
}

.tab-button {
    padding: var(--spacing-sm) var(--spacing-lg);
    background: transparent;
    color: var(--text-light);
    border: none;
    border-bottom: 3px solid transparent;
    border-radius: 0;
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    white-space: nowrap;
    transition: color 0.2s, border-color 0.2s, background-color 0.2s;
    box-shadow: none;
    margin-bottom: -2px;
    flex-shrink: 0;
}

.tab-button:hover {
    color: var(--text-color);
    background: var(--primary-light);
    transform: none;
    box-shadow: none;
}

.tab-button.active {
    color: var(--text-color);
    background: var(--card-bg);
    transform: none;
    box-shadow: none;
}

/* Language-specific active accent colors */
.tab-button[data-lang="python"].active {
    border-bottom-color: var(--python-color);
    color: var(--python-color);
}
.tab-button[data-lang="javascript"].active {
    border-bottom-color: #d4a017;
    color: #b8860b;
}
:root[data-theme="dark"] .tab-button[data-lang="javascript"].active {
    color: #fcd34d;
}
.tab-button[data-lang="csharp"].active {
    border-bottom-color: var(--csharp-color);
    color: var(--csharp-color);
}
:root[data-theme="dark"] .tab-button[data-lang="csharp"].active {
    color: #c084fc;
}

/* "All" button */
.tab-button-all {
    margin-left: auto;
    font-size: 0.8rem;
    padding: var(--spacing-sm) var(--spacing-md);
    color: var(--text-light);
}
.tab-button-all.active {
    border-bottom-color: var(--primary-color);
    color: var(--primary-color);
}

/* Tab content area */
.tab-content {
    position: relative;
}

.tab-content .tab-panel {
    padding: 0;
}

.tab-content .tab-panel pre {
    margin: 0;
    border: none;
    border-radius: 0;
}

/* Language label badges inside panels */
.tab-panel[data-lang="python"] pre {
    border-top: 2px solid var(--python-color);
}
.tab-panel[data-lang="javascript"] pre {
    border-top: 2px solid #d4a017;
}
.tab-panel[data-lang="csharp"] pre {
    border-top: 2px solid var(--csharp-color);
}

/* Show All mode — side by side grid */
.tab-content.show-all {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 0;
}

.tab-content.show-all .tab-panel {
    border-right: 1px solid var(--border-color);
}
.tab-content.show-all .tab-panel:last-child {
    border-right: none;
}

/* Per-panel copy button */
.tab-panel-inner {
    position: relative;
}

.tab-copy-button {
    position: absolute;
    top: 8px;
    right: 8px;
    padding: 3px 8px;
    background: var(--text-light);
    color: #fff;
    border: none;
    border-radius: 4px;
    font-size: 0.7rem;
    cursor: pointer;
    opacity: 0.6;
    transition: opacity 0.2s, background-color 0.2s;
    z-index: 10;
    box-shadow: none;
}
.tab-copy-button:hover {
    opacity: 1;
    background: var(--primary-color);
    transform: none;
    box-shadow: none;
}
.tab-copy-button.copy-ok { background: var(--success-border); opacity: 1; }
.tab-copy-button.copy-fail { background: var(--danger-border); opacity: 1; }

/* ===========================
   Instructor Notes
   =========================== */

.instructor-note {
    background: linear-gradient(135deg, rgba(99, 102, 241, 0.06) 0%, rgba(139, 92, 246, 0.06) 100%);
    border: 1px dashed var(--primary-color);
    border-radius: var(--radius-md);
    padding: var(--spacing-md) var(--spacing-lg);
    margin: var(--spacing-md) 0;
}

.instructor-note summary {
    cursor: pointer;
    font-weight: 700;
    color: var(--primary-color);
    user-select: none;
    font-size: 0.95rem;
}

.instructor-note .note-content {
    margin-top: var(--spacing-sm);
    padding-top: var(--spacing-sm);
    border-top: 1px solid var(--border-color);
    font-size: 0.92rem;
    color: var(--text-light);
}

/* ===========================
   Language Badges
   =========================== */

.lang-badge {
    display: inline-block;
    padding: 2px 8px;
    border-radius: 4px;
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.lang-badge-python {
    background: var(--python-bg);
    color: var(--python-color);
}
.lang-badge-javascript {
    background: var(--javascript-bg);
    color: #b8860b;
}
:root[data-theme="dark"] .lang-badge-javascript {
    color: #fcd34d;
}
.lang-badge-csharp {
    background: var(--csharp-bg);
    color: var(--csharp-color);
}
:root[data-theme="dark"] .lang-badge-csharp {
    color: #c084fc;
}

/* ===========================
   Comparison Table
   =========================== */

.comparison-table th:nth-child(2) { background: var(--python-color); }
.comparison-table th:nth-child(3) { background: #b8860b; }
.comparison-table th:nth-child(4) { background: var(--csharp-color); }

/* ===========================
   Responsive Design
   =========================== */

@media (min-width: 768px) {
    body { padding: var(--spacing-lg); }
    h1 { font-size: 2.25rem; }
    h2 { font-size: 1.8rem; }
    .container { padding: 0 var(--spacing-lg); }
    .card-grid {
        display: grid;
        grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
        gap: var(--spacing-lg);
    }
}

@media (min-width: 1024px) {
    body { padding: var(--spacing-xl); }
    h1 { font-size: 2.5rem; }
    .container { padding: 0 var(--spacing-xl); }
}

@media (max-width: 767px) {
    .mobile-menu-toggle { display: block; }

    .nav-links {
        display: none;
        position: absolute;
        top: 100%;
        left: 0;
        right: 0;
        background: var(--nav-bg);
        border-top: 1px solid var(--border-color);
        flex-direction: column;
        padding: var(--spacing-md);
        box-shadow: var(--shadow-md);
        z-index: 300;
    }
    .nav-links.active { display: flex; }

    .nav-divider { display: none; }

    .lesson-nav { flex-direction: column; }
    .lesson-nav a { width: 100%; text-align: center; justify-content: center; }

    table { font-size: 0.875rem; }
    h1 { font-size: 1.6rem; }
    h2 { font-size: 1.35rem; }
    h3 { font-size: 1.15rem; }

    /* Code tabs: stack in show-all mode on mobile */
    .tab-content.show-all {
        grid-template-columns: 1fr;
    }
    .tab-content.show-all .tab-panel {
        border-right: none;
        border-bottom: 1px solid var(--border-color);
    }
    .tab-content.show-all .tab-panel:last-child {
        border-bottom: none;
    }

    /* Smaller tab buttons on mobile */
    .tab-button {
        padding: var(--spacing-sm) var(--spacing-md);
        font-size: 0.82rem;
    }
    .tab-bar-title {
        display: none;
    }
}

/* ===========================
   Print Styles
   =========================== */

@media print {
    body { background: #fff; color: #000; }
    nav, .lesson-nav, .progress-indicator, .skip-to-main,
    .mobile-menu-toggle, .copy-button, .tab-copy-button,
    button, #theme-toggle { display: none !important; }
    h1, h2, h3, h4, h5, h6 {
        background: none !important;
        color: #000 !important;
        page-break-after: avoid;
    }
    a { color: #000; text-decoration: underline; }
    pre { page-break-inside: avoid; border: 1px solid #ccc; }
    img { page-break-inside: avoid; }
    .card { box-shadow: none; border: 1px solid #ccc; }

    /* Print all code tabs */
    .tab-bar { display: none; }
    .tab-content { display: block !important; }
    .tab-content .tab-panel {
        display: block !important;
        page-break-inside: avoid;
        margin-bottom: 1rem;
    }
    .tab-content .tab-panel::before {
        content: attr(data-label);
        display: block;
        font-weight: 700;
        margin-bottom: 0.25rem;
    }
}

/* ===========================
   Accessibility
   =========================== */

@media (prefers-contrast: high) {
    :root {
        --primary-color: #0052cc;
        --text-color: #000;
        --bg-color: #fff;
        --border-color: #000;
    }
}

@media (prefers-reduced-motion: reduce) {
    * {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
        scroll-behavior: auto !important;
    }
}

.keyboard-nav *:focus {
    outline: 3px solid var(--primary-color) !important;
    outline-offset: 2px !important;
}

/* ===========================
   Scrollbar
   =========================== */

::-webkit-scrollbar { width: 8px; height: 8px; }
::-webkit-scrollbar-track { background: var(--bg-color); }
::-webkit-scrollbar-thumb { background: var(--text-light); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: var(--primary-color); }
* { scrollbar-width: thin; scrollbar-color: var(--text-light) var(--bg-color); }

/* Touch UX */
* { -webkit-tap-highlight-color: rgba(0,0,0,0.08); }