/* ===== Общие стили ===== */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

:root {
    --primary: #2c6fbb;
    --primary-dark: #1a4f8a;
    --primary-light: #e8f0fe;
    --accent: #f39c12;
    --accent-dark: #e67e22;
    --text: #2c3e50;
    --text-light: #7f8c8d;
    --bg: #f5f7fa;
    --bg-card: #ffffff;
    --border: #dce1e8;
    --success: #27ae60;
    --warning: #e74c3c;
    --shadow: 0 4px 20px rgba(0,0,0,0.08);
    --radius: 12px;
    --radius-sm: 8px;
    --font-sans: 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    --font-mono: 'Cascadia Code', 'Fira Code', 'Consolas', 'Monaco', monospace;
    --scroll-margin: 120px;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-sans);
    background: var(--bg);
    color: var(--text);
    line-height: 1.6;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* ===== Skip Link (Accessibility) ===== */
.skip-link {
    position: absolute;
    top: -100%;
    left: 16px;
    background: var(--primary);
    color: #fff;
    padding: 8px 16px;
    border-radius: var(--radius-sm);
    z-index: 1000;
    font-weight: 600;
    text-decoration: none;
    transition: top 0.2s;
}

.skip-link:focus {
    top: 8px;
}

/* ===== Фокус-стили (Accessibility) ===== */
:focus-visible {
    outline: 3px solid var(--accent);
    outline-offset: 2px;
}

/* ===== Шапка ===== */
header {
    background: var(--primary-dark);
    color: #fff;
    padding: 0;
    box-shadow: 0 2px 10px rgba(0,0,0,0.15);
    position: sticky;
    top: 0;
    z-index: 100;
}

.header-top {
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 16px 24px;
    max-width: 1200px;
    margin: 0 auto;
    width: 100%;
}

.header-top .site-title {
    font-size: 1.35rem;
    font-weight: 700;
    letter-spacing: 0.02em;
}

.header-top a {
    color: #fff;
    text-decoration: none;
}

.header-top a:hover {
    opacity: 0.9;
}

/* Навигация */
nav {
    background: var(--primary);
    padding: 0;
    width: 100%;
}

nav ul {
    list-style: none;
    display: flex;
    justify-content: center;
    gap: 0;
    overflow-x: auto;
    padding: 0;
    max-width: 1200px;
    margin: 0 auto;
    -webkit-overflow-scrolling: touch;
    scrollbar-width: thin;
}

nav ul li {
    flex-shrink: 0;
}

nav ul li a {
    color: rgba(255,255,255,0.9);
    text-decoration: none;
    padding: 10px 20px;
    font-size: 0.9rem;
    font-weight: 500;
    border-radius: 0;
    transition: background 0.2s, color 0.2s;
    white-space: nowrap;
    display: block;
    border-bottom: 3px solid transparent;
}

nav ul li a:hover {
    background: rgba(255,255,255,0.1);
    color: #fff;
}

nav ul li a.active {
    color: #fff;
    border-bottom-color: var(--accent);
    background: rgba(255,255,255,0.08);
}

/* ===== Основной контент ===== */
main {
    flex: 1;
    max-width: 1000px;
    margin: 0 auto;
    padding: 28px 20px;
    width: 100%;
}

main > .page-title,
main > .page-subtitle {
    scroll-margin-top: var(--scroll-margin);
}

.card[id] {
    scroll-margin-top: var(--scroll-margin);
}

/* ===== Подвал ===== */
footer {
    background: var(--primary-dark);
    color: rgba(255,255,255,0.7);
    text-align: center;
    padding: 16px 20px;
    font-size: 0.85rem;
    margin-top: auto;
}

footer a {
    color: rgba(255,255,255,0.9);
}

/* ===== Хлебные крошки ===== */
.breadcrumbs {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 4px;
    margin-bottom: 16px;
    font-size: 0.85rem;
    color: var(--text-light);
    background: none;
    padding: 0;
    width: auto;
    max-width: none;
}

.breadcrumbs a {
    color: var(--primary);
    text-decoration: none;
}

.breadcrumbs a:hover {
    text-decoration: underline;
}

.breadcrumbs .separator {
    margin: 0 4px;
    color: var(--border);
}

.breadcrumbs .current {
    color: var(--text);
    font-weight: 500;
}

/* ===== Компоненты ===== */
.page-title {
    font-size: 2rem;
    color: var(--primary);
    margin-bottom: 8px;
    font-weight: 700;
}

.page-subtitle {
    color: var(--text-light);
    margin-bottom: 28px;
    font-size: 1.05rem;
    border-bottom: 2px solid var(--border);
    padding-bottom: 12px;
}

.section-title {
    font-size: 1.4rem;
    color: var(--primary-dark);
    margin: 24px 0 12px;
    padding-left: 12px;
    border-left: 4px solid var(--accent);
}

.section-subtitle {
    font-size: 1.1rem;
    color: var(--primary);
    margin: 18px 0 10px;
}

.text-light {
    color: var(--text-light);
}

.card {
    background: var(--bg-card);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    padding: 20px 24px;
    margin-bottom: 20px;
    border: 1px solid var(--border);
}

.card-title {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--primary);
    margin-bottom: 10px;
}

.info-box {
    background: var(--primary-light);
    border-left: 4px solid var(--primary);
    padding: 14px 18px;
    margin: 12px 0;
    border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}

.warning-box {
    background: #fef9e7;
    border-left: 4px solid var(--accent);
    padding: 14px 18px;
    margin: 12px 0;
    border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}

.danger-box {
    background: #fdedec;
    border-left: 4px solid var(--warning);
    padding: 14px 18px;
    margin: 12px 0;
    border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}

/* ===== Сетка карточек (главная) ===== */
.theme-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 20px;
    margin-top: 20px;
}

.theme-card {
    background: var(--bg-card);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    padding: 22px;
    border: 1px solid var(--border);
    transition: transform 0.3s, box-shadow 0.3s;
    display: flex;
    flex-direction: column;
}

a.theme-card {
    color: inherit;
    text-decoration: none;
}

.theme-card:hover {
    transform: translateY(-4px);
    box-shadow: 0 8px 30px rgba(0,0,0,0.12);
}

.theme-card .section-badge {
    display: inline-block;
    background: var(--accent);
    color: #fff;
    padding: 2px 10px;
    border-radius: 12px;
    font-size: 0.75rem;
    font-weight: 600;
    margin-bottom: 8px;
    align-self: flex-start;
}

.theme-card h3 {
    font-size: 1.1rem;
    color: var(--primary);
    margin-bottom: 8px;
}

.theme-card p {
    color: var(--text-light);
    font-size: 0.9rem;
    flex: 1;
    margin-bottom: 12px;
}

/* ===== Сетки карточек для главной ===== */
.class-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 24px;
    margin-top: 30px;
}

.class-card {
    text-align: center;
    padding: 30px 20px;
}

.class-card .class-icon {
    font-size: 3rem;
    margin-bottom: 10px;
}

.class-card h3 {
    font-size: 1.4rem;
    margin-bottom: 12px;
}

.class-card .class-hours {
    color: var(--text-light);
    margin-bottom: 8px;
}

.class-card .section-list {
    list-style: none;
    padding: 0;
    text-align: left;
    font-size: 0.9rem;
    color: var(--text-light);
}

.class-card .section-list li {
    margin-bottom: 2px;
}

/* ===== Таблицы ===== */
.table-wrap {
    overflow-x: auto;
    margin: 12px 0;
}

table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.95rem;
}

table th, table td {
    padding: 10px 14px;
    border: 1px solid var(--border);
    text-align: left;
}

table th {
    background: var(--primary);
    color: #fff;
    font-weight: 600;
}

table tr:nth-child(even) {
    background: var(--bg);
}

table tr:hover {
    background: var(--primary-light);
}

/* ===== Списки ===== */
.content-list {
    padding-left: 24px;
    margin: 8px 0;
}

.content-list li {
    margin-bottom: 6px;
}

/* ===== Блоки кода ===== */
.code-block {
    background: #1e1e2e;
    color: #cdd6f4;
    padding: 16px 20px;
    border-radius: var(--radius-sm);
    font-family: var(--font-mono);
    font-size: 0.9rem;
    line-height: 1.5;
    overflow-x: auto;
    margin: 10px 0;
    white-space: pre;
    tab-size: 4;
}

.code-block .comment {
    color: #6c7086;
}

.code-block .keyword {
    color: #cba6f7;
}

.code-block .string {
    color: #a6e3a1;
}

.code-block .number {
    color: #fab387;
}

.code-block .function {
    color: #89b4fa;
}

.code-inline {
    background: #eef1f5;
    padding: 2px 6px;
    border-radius: 4px;
    font-family: var(--font-mono);
    font-size: 0.88em;
    color: #c7254e;
}

pre {
    background: #1e1e2e;
    color: #cdd6f4;
    padding: 16px 20px;
    border-radius: var(--radius-sm);
    font-family: var(--font-mono);
    font-size: 0.9rem;
    line-height: 1.5;
    overflow-x: auto;
    margin: 10px 0;
}

/* ===== Интерактивные блоки ===== */
.interactive-block {
    background: linear-gradient(135deg, #f8f9fa, #e9ecef);
    border: 2px dashed var(--primary);
    border-radius: var(--radius);
    padding: 20px;
    margin: 16px 0;
}

.interactive-block h4 {
    color: var(--primary);
    margin-bottom: 12px;
    font-size: 1rem;
}

.interactive-block label {
    display: block;
    margin-bottom: 6px;
    font-weight: 500;
    font-size: 0.9rem;
}

.interactive-block input,
.interactive-block select {
    padding: 8px 12px;
    border: 2px solid var(--border);
    border-radius: var(--radius-sm);
    font-size: 1rem;
    width: 100%;
    max-width: 300px;
    margin-bottom: 10px;
    transition: border-color 0.3s;
}

.interactive-block input:focus,
.interactive-block select:focus {
    border-color: var(--primary);
}

.btn {
    display: inline-block;
    padding: 8px 20px;
    background: var(--primary);
    color: #fff;
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 0.95rem;
    transition: background 0.3s;
}

.btn:hover {
    background: var(--primary-dark);
}

.btn:focus-visible {
    outline: 3px solid var(--accent);
    outline-offset: 2px;
}

.btn-accent {
    background: var(--accent);
}

.btn-accent:hover {
    background: var(--accent-dark);
}

.btn-completed {
    background: var(--success) !important;
}

.result-box {
    background: #fff;
    border: 2px solid var(--success);
    border-radius: var(--radius-sm);
    padding: 12px 16px;
    margin-top: 10px;
    font-size: 1.05rem;
    font-weight: 500;
    display: none;
}

.result-box.show {
    display: block;
}

/* ===== Тесты ===== */
.quiz-block {
    background: var(--bg-card);
    border: 2px solid var(--primary-light);
    border-radius: var(--radius);
    padding: 20px 24px;
    margin: 16px 0;
}

.quiz-block fieldset {
    border: none;
    padding: 0;
    margin: 0;
}

.quiz-block legend {
    font-size: 1.05rem;
    font-weight: 600;
    color: var(--primary);
    margin-bottom: 16px;
    width: 100%;
}

.quiz-question {
    margin-bottom: 16px;
    padding-bottom: 12px;
    border-bottom: 1px solid var(--border);
}

.quiz-question:last-of-type {
    border-bottom: none;
    margin-bottom: 8px;
}

.quiz-question p {
    font-weight: 500;
    margin-bottom: 8px;
}

.quiz-question label {
    display: block;
    padding: 4px 0;
    font-size: 0.95rem;
    cursor: pointer;
}

.quiz-question input[type="radio"] {
    margin-right: 8px;
}

.quiz-result {
    font-weight: 600;
    font-size: 1rem;
    margin-top: 12px;
    padding: 10px 16px;
    border-radius: var(--radius-sm);
    display: none;
}

.quiz-result.show {
    display: block;
}

/* ===== Динамический тест (по одному вопросу) ===== */
.dynamic-quiz .quiz-header h4 {
    margin: 0 0 12px 0;
    color: var(--primary);
    font-size: 1.15rem;
}

.dynamic-quiz .quiz-counter {
    font-size: 0.9rem;
    color: var(--text-light);
    margin-bottom: 16px;
    font-weight: 500;
}

.dynamic-quiz .quiz-loading,
.dynamic-quiz .quiz-empty {
    text-align: center;
    padding: 20px;
    color: var(--text-light);
    font-style: italic;
}

.dynamic-quiz .quiz-body {
    min-height: 120px;
}

.dynamic-quiz .quiz-question-text {
    font-weight: 600;
    font-size: 1.05rem;
    margin-bottom: 16px;
    line-height: 1.5;
}

.dynamic-quiz .quiz-options {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.dynamic-quiz .quiz-option {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 10px 14px;
    border: 2px solid var(--border);
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: border-color 0.2s, background 0.2s;
    font-size: 0.95rem;
}

.dynamic-quiz .quiz-option:hover {
    border-color: var(--primary-light);
    background: var(--bg-secondary);
}

.dynamic-quiz .quiz-option input[type="radio"] {
    margin: 0;
    flex-shrink: 0;
}

.dynamic-quiz .quiz-option-letter {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 26px;
    height: 26px;
    border-radius: 50%;
    background: var(--bg-secondary);
    font-weight: 700;
    font-size: 0.85rem;
    color: var(--primary);
    flex-shrink: 0;
    border: 1px solid var(--border);
}

.dynamic-quiz .quiz-option.correct {
    border-color: var(--success);
    background: rgba(39, 174, 96, 0.08);
}

.dynamic-quiz .quiz-option.correct .quiz-option-letter {
    background: var(--success);
    color: #fff;
    border-color: var(--success);
}

.dynamic-quiz .quiz-option.wrong {
    border-color: var(--warning);
    background: rgba(231, 76, 60, 0.08);
}

.dynamic-quiz .quiz-option.wrong .quiz-option-letter {
    background: var(--warning);
    color: #fff;
    border-color: var(--warning);
}

.dynamic-quiz .quiz-nav {
    display: flex;
    justify-content: flex-end;
    gap: 8px;
    margin-top: 20px;
    padding-top: 16px;
    border-top: 1px solid var(--border);
}

.dynamic-quiz .quiz-btn-prev {
    background: var(--bg-secondary);
    color: var(--text);
    border: 1px solid var(--border);
}

.dynamic-quiz .quiz-btn-prev:hover {
    border-color: var(--primary);
}

.dynamic-quiz .quiz-final-result {
    display: none;
}

.dynamic-quiz .quiz-final-result:not(:empty) {
    display: block;
}

.dynamic-quiz .quiz-result-card {
    text-align: center;
}

.dynamic-quiz .quiz-result-card h4 {
    margin: 0 0 16px 0;
    color: var(--primary);
}

.dynamic-quiz .quiz-score {
    font-size: 2.5rem;
    font-weight: 700;
    margin: 12px 0;
    line-height: 1;
}

.dynamic-quiz .quiz-score-num {
    color: var(--primary);
}

.dynamic-quiz .quiz-score-sep {
    color: var(--text-light);
}

.dynamic-quiz .quiz-score-total {
    color: var(--text-light);
}

.dynamic-quiz .quiz-score-bar {
    width: 100%;
    max-width: 300px;
    height: 10px;
    background: var(--bg-secondary);
    border-radius: 5px;
    margin: 16px auto;
    overflow: hidden;
}

.dynamic-quiz .quiz-score-fill {
    height: 100%;
    background: var(--primary);
    border-radius: 5px;
    transition: width 0.5s ease;
}

.dynamic-quiz .quiz-verdict {
    font-size: 1.05rem;
    font-weight: 600;
    margin: 12px 0 20px;
}

.dynamic-quiz .quiz-verdict-excellent {
    color: var(--success);
}

.dynamic-quiz .quiz-verdict-good {
    color: var(--accent);
}

.dynamic-quiz .quiz-verdict-low {
    color: var(--warning);
}

.dynamic-quiz .quiz-wrong-list {
    text-align: left;
    max-width: 500px;
    margin: 20px auto;
    background: var(--bg-secondary);
    border-radius: var(--radius-sm);
    padding: 16px 20px;
}

.dynamic-quiz .quiz-wrong-list h5 {
    margin: 0 0 12px 0;
    font-size: 0.95rem;
    color: var(--text);
}

.dynamic-quiz .quiz-wrong-item {
    margin-bottom: 12px;
    padding-bottom: 12px;
    border-bottom: 1px solid var(--border);
}

.dynamic-quiz .quiz-wrong-item:last-child {
    margin-bottom: 0;
    padding-bottom: 0;
    border-bottom: none;
}

.dynamic-quiz .quiz-wrong-q {
    font-weight: 500;
    margin: 0 0 4px 0;
    font-size: 0.9rem;
}

.dynamic-quiz .quiz-wrong-a {
    margin: 0;
    color: var(--success);
    font-size: 0.9rem;
}

.dynamic-quiz .quiz-btn-retry {
    margin-top: 20px;
}

.dynamic-quiz .quiz-check {
    color: var(--success);
    font-weight: 700;
    margin-left: 4px;
}

.dynamic-quiz .quiz-cross {
    color: var(--warning);
    font-weight: 700;
    margin-left: 4px;
}

.dynamic-quiz .quiz-explanation {
    margin-top: 16px;
    padding: 12px 16px;
    border-radius: var(--radius-sm);
    font-size: 0.95rem;
    line-height: 1.5;
    animation: fadeInQuiz 0.3s ease;
}

.dynamic-quiz .quiz-explanation-correct {
    background: rgba(39, 174, 96, 0.08);
    border-left: 3px solid var(--success);
    color: var(--text);
}

.dynamic-quiz .quiz-explanation-wrong {
    background: rgba(231, 76, 60, 0.08);
    border-left: 3px solid var(--warning);
    color: var(--text);
}

.dynamic-quiz .quiz-explanation-icon {
    font-weight: 700;
}

@keyframes fadeInQuiz {
    from { opacity: 0; transform: translateY(-4px); }
    to { opacity: 1; transform: translateY(0); }
}

/* ===== Схемы / Иллюстрации ===== */
.scheme {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 16px;
    flex-wrap: wrap;
    padding: 16px;
    background: #fff;
    border-radius: var(--radius-sm);
    border: 1px solid var(--border);
    margin: 12px 0;
}

.scheme-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 6px;
}

.scheme-box {
    background: var(--primary-light);
    border: 2px solid var(--primary);
    border-radius: var(--radius-sm);
    padding: 12px 18px;
    font-weight: 600;
    text-align: center;
    min-width: 80px;
}

.scheme-arrow {
    font-size: 1.5rem;
    color: var(--primary);
    font-weight: bold;
}

.scheme-label {
    font-size: 0.8rem;
    color: var(--text-light);
}

/* ===== RGB палитра ===== */
.rgb-preview {
    width: 150px;
    height: 150px;
    border-radius: var(--radius-sm);
    border: 2px solid var(--border);
    margin: 10px 0;
}

.rgb-slider {
    width: 100%;
    max-width: 300px;
    margin: 4px 0 10px;
}

/* ===== Главная страница ===== */
.hero {
    text-align: center;
    padding: 30px 20px;
    background: linear-gradient(135deg, var(--primary-light), #d4e6f9);
    border-radius: var(--radius);
    margin-bottom: 30px;
}

.hero h2 {
    font-size: 1.8rem;
    color: var(--primary-dark);
    margin-bottom: 10px;
}

.hero p {
    color: var(--text-light);
    max-width: 600px;
    margin: 0 auto;
    font-size: 1.05rem;
}

/* ===== Боковая навигация (оглавление) ===== */
.content-layout {
    display: flex;
    gap: 24px;
    position: relative;
    align-items: flex-start;
}

.content-layout .toc {
    width: 220px;
    flex-shrink: 0;
    position: sticky;
    top: 120px;
    align-self: flex-start;
    background: var(--bg-card);
    border-radius: var(--radius);
    padding: 18px 16px;
    border: 1px solid var(--border);
    font-size: 0.88em;
    max-height: calc(100vh - 100px);
    overflow-y: auto;
    box-shadow: var(--shadow);
    scroll-margin-top: var(--scroll-margin);
    z-index: 10;
}

.content-layout .toc::-webkit-scrollbar {
    width: 4px;
}

.content-layout .toc::-webkit-scrollbar-thumb {
    background: var(--border);
    border-radius: 2px;
}

.content-layout .toc-main {
    flex: 1;
    min-width: 0;
}

.toc-title {
    font-weight: 700;
    margin-bottom: 10px;
    color: var(--primary);
    font-size: 1em;
}

.toc ol {
    list-style: none;
    padding: 0;
    margin: 0;
}

.toc ol li {
    margin-bottom: 2px;
}

.toc ol li a {
    color: var(--text-light);
    text-decoration: none;
    display: block;
    padding: 4px 8px;
    border-radius: 4px;
    transition: color 0.2s, background 0.2s;
    font-size: 0.92em;
    line-height: 1.4;
}

.toc ol li a:hover {
    color: var(--primary);
    background: rgba(44, 111, 187, 0.06);
}

.toc ol li a.toc-active {
    color: var(--primary);
    font-weight: 600;
    background: rgba(44, 111, 187, 0.1);
}

/* ===== Навигация предыдущая/следующая тема ===== */
.topic-nav {
    display: flex;
    justify-content: space-between;
    gap: 16px;
    margin-top: 32px;
    padding-top: 20px;
    border-top: 2px solid var(--border);
    flex-wrap: wrap;
}

.topic-nav a {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 12px 20px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    text-decoration: none;
    color: var(--primary);
    font-weight: 500;
    font-size: 0.9rem;
    transition: all 0.3s;
    flex: 1;
    min-width: 200px;
}

.topic-nav a:hover {
    background: var(--primary-light);
    border-color: var(--primary);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(0,0,0,0.08);
}

.topic-nav .nav-prev {
    justify-content: flex-start;
}

.topic-nav .nav-next {
    justify-content: flex-end;
    text-align: right;
}

.topic-nav .nav-label {
    display: block;
    font-size: 0.75rem;
    color: var(--text-light);
    font-weight: 400;
}

.topic-nav .nav-title {
    display: block;
    font-weight: 600;
    font-size: 0.9rem;
}

/* ===== Прогресс изучения ===== */
.progress-bar-container {
    background: var(--border);
    border-radius: 10px;
    height: 6px;
    margin: 8px 0 20px;
    overflow: hidden;
}

.progress-bar {
    background: linear-gradient(90deg, var(--primary), var(--success));
    height: 100%;
    border-radius: 10px;
    transition: width 0.5s ease;
    width: 0;
}

.progress-text {
    font-size: 0.8rem;
    color: var(--text-light);
    margin-bottom: 4px;
}

/* ===== Исполнитель (блок-схема алгоритма) ===== */
.executor-visual {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 8px;
    padding: 16px;
    background: #fff;
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    margin: 12px 0;
}

.executor-visual .grid-canvas {
    display: grid;
    gap: 1px;
    background: #ccc;
    border: 2px solid var(--text);
}

.executor-visual .grid-canvas .cell {
    width: 24px;
    height: 24px;
    background: #fff;
}

.executor-visual .grid-canvas .cell.filled {
    background: var(--primary);
}

/* ===== Кнопка "Наверх" ===== */
.back-to-top {
    position: fixed;
    bottom: 24px;
    right: 24px;
    width: 48px;
    height: 48px;
    border-radius: 50%;
    background: var(--primary);
    color: #fff;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    box-shadow: 0 4px 12px rgba(0,0,0,0.2);
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.3s, visibility 0.3s, transform 0.2s;
    z-index: 50;
    display: flex;
    align-items: center;
    justify-content: center;
}

.back-to-top.visible {
    opacity: 1;
    visibility: visible;
}

.back-to-top:hover {
    background: var(--primary-dark);
    transform: translateY(-2px);
}

.back-to-top:focus-visible {
    outline: 3px solid var(--accent);
    outline-offset: 2px;
}

/* ===== Адаптивность ===== */
@media (max-width: 768px) {
    .header-top {
        padding: 12px 16px;
    }

    .header-top .site-title {
        font-size: 1.1rem;
    }

    nav ul li a {
        font-size: 0.82rem;
        padding: 8px 14px;
    }

    .page-title {
        font-size: 1.5rem;
    }

    .theme-grid {
        grid-template-columns: 1fr;
    }

    .scheme {
        gap: 8px;
    }

    .scheme-box {
        padding: 8px 12px;
        min-width: 60px;
        font-size: 0.9rem;
    }

    .topic-nav {
        flex-direction: column;
    }

    .topic-nav a {
        min-width: unset;
    }

    .breadcrumbs {
        font-size: 0.78rem;
    }

    .back-to-top {
        bottom: 16px;
        right: 16px;
        width: 42px;
        height: 42px;
        font-size: 1.3rem;
    }

    /* Sidebar TOC — мобильная версия */
    .content-layout {
        flex-direction: column;
    }

    .content-layout .toc {
        width: 100%;
        position: relative;
        top: 0;
        max-height: none;
        overflow-y: visible;
    }

    .content-layout .toc ol {
        display: flex;
        flex-wrap: wrap;
        gap: 4px;
    }

    .content-layout .toc ol li {
        margin-bottom: 0;
    }

    .content-layout .toc ol li a {
        display: inline-block;
        background: var(--bg);
        padding: 4px 10px;
        border-radius: 20px;
        font-size: 0.82em;
    }

    .content-layout .toc ol li a.toc-active {
        background: var(--primary);
        color: #fff;
    }
}

@media (max-width: 480px) {
    main {
        padding: 16px 12px;
    }

    .card {
        padding: 14px 16px;
    }

    .interactive-block {
        padding: 14px;
    }

    .code-block, pre {
        font-size: 0.8rem;
        padding: 10px 12px;
    }
}

/* ===== Анимации ===== */
@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

main > .page-title,
main > .page-subtitle,
main > .hero {
    animation: fadeIn 0.4s ease-out;
}

/* Уважение к настройкам пользователя */
@media (prefers-reduced-motion: reduce) {
    *, *::before, *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
        scroll-behavior: auto !important;
    }
}

/* ===== Печать ===== */
@media print {
    header {
        position: static;
        box-shadow: none;
        background: #fff;
        color: #000;
        border-bottom: 2px solid #000;
    }

    nav {
        background: none;
    }

    nav ul li a {
        color: #000;
        border-bottom-color: transparent;
    }

    .header-top {
        padding: 8px 0;
    }

    .header-top .site-title,
    .header-top a {
        color: #000;
    }

    nav ul li a.active {
        border-bottom-color: #000;
    }

    .skip-link, .back-to-top {
        display: none !important;
    }

    footer {
        background: #fff;
        color: #666;
        border-top: 1px solid #ccc;
    }

    .interactive-block,
    .quiz-block,
    .topic-nav,
    .progress-bar-container,
    .progress-text,
    .btn {
        display: none !important;
    }

    .content-layout {
        display: block;
    }

    .content-layout .toc {
        position: static;
        width: auto;
        max-height: none;
        overflow: visible;
        border: none;
        box-shadow: none;
        padding: 0;
        background: none;
        margin-bottom: 16px;
    }

    .content-layout .toc ol {
        display: flex;
        flex-wrap: wrap;
        gap: 4px;
    }

    .content-layout .toc ol li a {
        color: #000;
        background: none;
        padding: 2px 4px;
    }

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

    .card {
        box-shadow: none;
        border: 1px solid #ccc;
        break-inside: avoid;
    }

    .theme-grid {
        display: block;
    }

    .theme-card {
        box-shadow: none;
        border: 1px solid #ccc;
        margin-bottom: 12px;
    }

    a[href]::after {
        content: " (" attr(href) ")";
        font-size: 0.8em;
        color: #666;
    }

    .breadcrumbs a::after {
        content: none;
    }
}

/* ===== Тёмная тема ===== */
@media (prefers-color-scheme: dark) {
    :root {
        --primary: #5b9bd5;
        --primary-dark: #3a7cc0;
        --primary-light: #1a2a3a;
        --accent: #f5a623;
        --accent-dark: #e09000;
        --text: #e0e6ed;
        --text-light: #8899aa;
        --bg: #0f1923;
        --bg-card: #1a2a3a;
        --border: #2a3a4a;
        --success: #2ecc71;
        --warning: #e74c3c;
        --shadow: 0 4px 20px rgba(0,0,0,0.3);
    }

    body {
        background: var(--bg);
        color: var(--text);
    }

    .code-block, .code-block pre, pre {
        background: #0d1117;
        color: #c9d1d9;
    }

    .code-inline {
        background: #1a2a3a;
        color: #f97583;
    }

    table tr:nth-child(even) {
        background: rgba(255,255,255,0.03);
    }

    table tr:hover {
        background: rgba(91,155,213,0.1);
    }

    .scheme {
        background: var(--bg-card);
    }

    .result-box {
        background: var(--bg-card);
    }

    .interactive-block {
        background: linear-gradient(135deg, #1a2a3a, #0f1923);
    }

    .hero {
        background: linear-gradient(135deg, #1a2a3a, #0f1923);
    }

    .toc {
        background: var(--bg-card);
    }

    .quiz-block {
        background: var(--bg-card);
    }

    .topic-nav a {
        background: var(--bg-card);
    }

    .rgb-preview {
        border-color: var(--border);
    }

    .warning-box {
        background: #2a2000;
    }

    .danger-box {
        background: #2a0a0a;
    }

    .btn-completed {
        background: var(--success) !important;
    }
}

/* ===== Переключатель темы ===== */
.theme-toggle {
    background: none;
    border: 2px solid rgba(255,255,255,0.3);
    color: inherit;
    cursor: pointer;
    padding: 6px 10px;
    border-radius: 8px;
    font-size: 1.1rem;
    line-height: 1;
    transition: all 0.2s;
    margin-left: 12px;
}
.theme-toggle:hover {
    border-color: rgba(255,255,255,0.6);
    background: rgba(255,255,255,0.1);
}
.header-top {
    display: flex;
    align-items: center;
    justify-content: space-between;
}
.header-top .site-title {
    flex: 1;
}

/* Тёмная тема по data-атрибуту */
html[data-theme="dark"] {
    --primary: #5b9bd5;
    --primary-dark: #3a7cc0;
    --primary-light: #1a2a3a;
    --accent: #f5a623;
    --accent-dark: #e09000;
    --text: #e0e6ed;
    --text-light: #8899aa;
    --bg: #0f1923;
    --bg-card: #1a2a3a;
    --border: #2a3a4a;
    --success: #2ecc71;
    --warning: #e74c3c;
    --shadow: 0 4px 20px rgba(0,0,0,0.3);
}
html[data-theme="dark"] body {
    background: var(--bg);
    color: var(--text);
}
html[data-theme="dark"] .code-block, html[data-theme="dark"] .code-block pre, html[data-theme="dark"] pre {
    background: #0d1117;
    color: #c9d1d9;
}
html[data-theme="dark"] .code-inline {
    background: #1a2a3a;
    color: #f97583;
}
html[data-theme="dark"] table tr:nth-child(even) {
    background: rgba(255,255,255,0.03);
}
html[data-theme="dark"] table tr:hover {
    background: rgba(91,155,213,0.1);
}
html[data-theme="dark"] .scheme {
    background: var(--bg-card);
}
html[data-theme="dark"] .result-box {
    background: var(--bg-card);
}
html[data-theme="dark"] .interactive-block {
    background: linear-gradient(135deg, #1a2a3a, #0f1923);
}
html[data-theme="dark"] .hero {
    background: linear-gradient(135deg, #1a2a3a, #0f1923);
}
html[data-theme="dark"] .toc {
    background: var(--bg-card);
}
html[data-theme="dark"] .quiz-block {
    background: var(--bg-card);
}
html[data-theme="dark"] .topic-nav a {
    background: var(--bg-card);
}
html[data-theme="dark"] .rgb-preview {
    border-color: var(--border);
}
html[data-theme="dark"] .warning-box {
    background: #2a2000;
}
html[data-theme="dark"] .danger-box {
    background: #2a0a0a;
}
html[data-theme="dark"] .btn-completed {
    background: var(--success) !important;
}

/* Светлая тема по data-атрибуту */
html[data-theme="light"] {
    --primary: #2c5aa0;
    --primary-dark: #1e3f73;
    --primary-light: #e8f0fe;
    --accent: #e67e22;
    --accent-dark: #d35400;
    --text: #2c3e50;
    --text-light: #7f8c8d;
    --bg: #f5f7fa;
    --bg-card: #ffffff;
    --border: #e0e4e8;
    --success: #27ae60;
    --warning: #e74c3c;
    --shadow: 0 4px 20px rgba(0,0,0,0.08);
}