/* ===========================
   Course Template - Main CSS
   Mobile-first, Responsive, Accessible
   Updated: 2026 — dark/light mode, modern layout
   Shared design system from python_intro
   =========================== */

/* ===========================
   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 {
    --bg-color: #f8fafc;
    --card-bg: #ffffff;
    --nav-bg: #ffffff;
    --text-color: #1e293b;
    --text-light: #64748b;
    --border-color: #e2e8f0;
    --primary-color: #3b82f6;
    --primary-hover: #2563eb;
    --primary-light: rgba(59, 130, 246, 0.08);
    --primary-gradient: linear-gradient(135deg, #3b82f6 0%, #6366f1 100%);
    --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;
    --success-color: #22c55e;
    --warning-bg: #fffbeb;
    --warning-border: #f59e0b;
    --warning-color: #f59e0b;
    --info-bg: #eff6ff;
    --info-border: #3b82f6;
    --danger-bg: #fef2f2;
    --danger-border: #ef4444;
    --accent-color: #3b82f6;
    --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-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-xxl: 3rem;
    --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;
    --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);
    --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;
    --success-color: #22c55e;
    --warning-bg: rgba(245, 158, 11, 0.1);
    --warning-border: #f59e0b;
    --warning-color: #f59e0b;
    --info-bg: rgba(59, 130, 246, 0.1);
    --info-border: #3b82f6;
    --danger-bg: rgba(239, 68, 68, 0.1);
    --danger-border: #ef4444;
    --accent-color: #6366f1;
    --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);
}

@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);
        --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); --warning-bg: rgba(245, 158, 11, 0.1);
        --info-bg: rgba(59, 130, 246, 0.1); --danger-bg: rgba(239, 68, 68, 0.1);
        --accent-color: #6366f1;
        --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);
    }
}

: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);
    --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; --warning-bg: #fffbeb; --info-bg: #eff6ff; --danger-bg: #fef2f2;
    --accent-color: #3b82f6;
    --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 */
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; }
.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 */
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 { 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 { 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); }
.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; }

/* Utilities */
.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; }
.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 { 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 */
.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 */
.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; }

/* TOC
   Open: full sticky card under the nav
   Closed: small floating action button (FAB) in upper-left, just below nav */
.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, box-shadow 0.3s ease, transform 0.2s ease;
}
.toc-card summary { list-style: none; }
.toc-card summary::-webkit-details-marker { display: none; }
.toc-card summary::marker { content: ''; }
.toc-card summary {
    cursor: pointer;
    font-weight: 700;
    padding: var(--spacing-sm) var(--spacing-md);
    user-select: none;
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}
.toc-card .toc-icon { font-size: 1.25rem; line-height: 1; }
.toc-card .toc-label { font-size: 1.1rem; font-weight: 700; }
.toc-card .toc-chevron {
    margin-left: auto;
    font-size: 0.85rem;
    color: var(--text-light);
    transition: transform 0.3s ease;
}
.toc-card[open] .toc-chevron { transform: rotate(180deg); }
.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; }

/* Collapsed state: FAB upper-left, just below nav */
.toc-card:not([open]) {
    position: fixed;
    top: 76px;
    left: var(--spacing-lg);
    bottom: auto;
    right: auto;
    width: 44px;
    height: 44px;
    padding: 0;
    margin: 0;
    border: none;
    border-radius: 50%;
    background: var(--primary-color);
    box-shadow: var(--shadow-md);
    z-index: 150;
    overflow: hidden;
}
.toc-card:not([open]):hover {
    transform: scale(1.08);
    background: var(--primary-hover);
    box-shadow: var(--shadow-lg);
}
.toc-card:not([open]) summary {
    width: 100%;
    height: 100%;
    padding: 0;
    justify-content: center;
    color: #fff;
}
.toc-card:not([open]) .toc-icon { font-size: 1.25rem; color: #fff; }
.toc-card:not([open]) .toc-label,
.toc-card:not([open]) .toc-chevron {
    position: absolute;
    width: 1px; height: 1px;
    padding: 0; margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}
@media (max-width: 767px) {
    .toc-card:not([open]) {
        top: 68px;
        left: var(--spacing-md);
        width: 40px; height: 40px;
    }
    .toc-card:not([open]) .toc-icon { font-size: 1.1rem; }
}

/* Quiz */
.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 / Mermaid */
: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 */
#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); } }

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

/* Responsive */
@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; } }

/* Print */
@media print { body { background: #fff; color: #000; } nav, .lesson-nav, .progress-indicator, .skip-to-main, .mobile-menu-toggle, .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; } }

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