/* 
 * Математический тренажёр — Стили
 * Современный дизайн с тёмной темой и анимациями
 */

/* ============================================
   CSS Variables (Токены дизайна)
   ============================================ */
:root {
    /* Цвета */
    --bg-primary: #0f0f1a;
    --bg-secondary: #1a1a2e;
    --bg-tertiary: #252542;
    --bg-card: #1e1e35;

    --text-primary: #ffffff;
    --text-secondary: #a0a0b8;
    --text-muted: #6b6b80;

    --accent-primary: #6366f1;
    --accent-secondary: #818cf8;
    --accent-gradient: linear-gradient(135deg, #6366f1 0%, #a855f7 100%);

    --success: #10b981;
    --success-bg: rgba(16, 185, 129, 0.15);
    --error: #ef4444;
    --error-bg: rgba(239, 68, 68, 0.15);
    --warning: #f59e0b;

    /* Размеры */
    --sidebar-width: 280px;
    --border-radius: 12px;
    --border-radius-sm: 8px;

    /* Тени */
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 20px rgba(0, 0, 0, 0.4);
    --shadow-lg: 0 8px 40px rgba(0, 0, 0, 0.5);
    --shadow-glow: 0 0 30px rgba(99, 102, 241, 0.3);

    /* Переходы */
    --transition-fast: 0.15s ease;
    --transition-normal: 0.25s ease;
    --transition-slow: 0.4s ease;
}

/* ============================================
   Reset & Base
   ============================================ */
*,
*::before,
*::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
    scroll-behavior: smooth;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    display: flex;
}

a {
    color: inherit;
    text-decoration: none;
}

button {
    font-family: inherit;
    cursor: pointer;
    border: none;
    background: none;
}

ul {
    list-style: none;
}

/* ============================================
   Layout
   ============================================ */
.sidebar {
    width: var(--sidebar-width);
    height: 100vh;
    position: fixed;
    left: 0;
    top: 0;
    background: var(--bg-secondary);
    border-right: 1px solid rgba(255, 255, 255, 0.05);
    display: flex;
    flex-direction: column;
    overflow-y: auto;
    z-index: 100;
}

.main-content {
    margin-left: var(--sidebar-width);
    flex: 1;
    min-height: 100vh;
    padding: 2rem;
}

.content-container {
    max-width: 900px;
    margin: 0 auto;
}

/* ============================================
   Sidebar
   ============================================ */
.sidebar-header {
    padding: 1.5rem;
    border-bottom: 1px solid rgba(255, 255, 255, 0.05);
}

.logo {
    font-size: 1.25rem;
    font-weight: 700;
    background: var(--accent-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.nav-menu {
    padding: 1rem 0;
    flex: 1;
}

.nav-item,
.nav-subitem {
    display: flex;
    align-items: center;
    padding: 0.75rem 1.5rem;
    color: var(--text-secondary);
    transition: all var(--transition-fast);
}

.nav-item:hover,
.nav-subitem:hover {
    background: rgba(99, 102, 241, 0.1);
    color: var(--text-primary);
}

.nav-item.active,
.nav-subitem.active {
    background: rgba(99, 102, 241, 0.15);
    color: var(--accent-secondary);
    border-right: 3px solid var(--accent-primary);
}

.nav-home {
    font-weight: 500;
    margin-bottom: 0.5rem;
}

.nav-section {
    margin-top: 0.25rem;
}

.nav-section-toggle {
    width: 100%;
    display: flex;
    align-items: center;
    gap: 0.75rem;
    padding: 0.75rem 1.5rem;
    color: var(--text-secondary);
    font-size: 0.875rem;
    text-align: left;
    transition: all var(--transition-fast);
}

.nav-section-toggle:hover {
    background: rgba(255, 255, 255, 0.03);
    color: var(--text-primary);
}

.section-icon {
    font-size: 1rem;
}

.section-title {
    flex: 1;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.toggle-icon {
    font-size: 0.625rem;
    transition: transform var(--transition-fast);
}

.nav-section.open .toggle-icon {
    transform: rotate(180deg);
}

.nav-section-content {
    display: none;
    padding-left: 1rem;
}

.nav-section.open .nav-section-content {
    display: block;
}

.nav-subitem {
    padding: 0.5rem 1.5rem;
    font-size: 0.875rem;
}

.section-link {
    font-weight: 500;
    color: var(--text-primary);
}

.level-link {
    color: var(--text-muted);
}

/* ============================================
   Welcome Section (Главная страница)
   ============================================ */
.welcome-section {
    padding: 2rem 0;
}

.welcome-header {
    text-align: center;
    margin-bottom: 3rem;
}

.welcome-title {
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: 0.75rem;
    background: var(--accent-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.welcome-subtitle {
    font-size: 1.125rem;
    color: var(--text-secondary);
}

.mobile-cta-btn {
    display: none;
    margin-top: 1.5rem;
    padding: 0.875rem 2.5rem;
    background: var(--accent-gradient);
    color: #fff;
    font-size: 1.125rem;
    font-weight: 600;
    border-radius: 30px;
    text-align: center;
    transition: all var(--transition-fast);
    box-shadow: var(--shadow-glow);
}

.mobile-cta-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 0 40px rgba(99, 102, 241, 0.4);
}

.feature-cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1.5rem;
    margin-bottom: 3rem;
}

.feature-card {
    background: var(--bg-card);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    text-align: center;
    border: 1px solid rgba(255, 255, 255, 0.05);
    transition: all var(--transition-normal);
}

.feature-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-md);
    border-color: rgba(99, 102, 241, 0.3);
}

.feature-icon {
    font-size: 2.5rem;
    margin-bottom: 1rem;
}

.feature-card h3 {
    font-size: 1.125rem;
    margin-bottom: 0.5rem;
}

.feature-card p {
    font-size: 0.875rem;
    color: var(--text-secondary);
}

/* ============================================
   SEO Article (Главная страница — текстовый контент)
   ============================================ */
.seo-article {
    margin-bottom: 3rem;
}

.article-section {
    margin-bottom: 2.5rem;
}

.article-section h2 {
    font-size: 1.375rem;
    font-weight: 700;
    margin-bottom: 1rem;
    color: var(--text-primary);
    line-height: 1.3;
}

.article-section h3 {
    font-size: 1.125rem;
    font-weight: 600;
    margin-top: 1.5rem;
    margin-bottom: 0.75rem;
    color: var(--accent-secondary);
}

.article-section p {
    font-size: 1rem;
    line-height: 1.75;
    color: var(--text-secondary);
    margin-bottom: 1rem;
}

.article-section p:last-child {
    margin-bottom: 0;
}

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

.article-section em {
    color: var(--accent-secondary);
    font-style: normal;
    font-weight: 500;
}

.levels-cta-text {
    text-align: center;
    margin-bottom: 1.5rem;
}

.levels-cta-text p {
    font-size: 1.0625rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

.sections-overview h2 {
    font-size: 1.5rem;
    margin-bottom: 1.5rem;
}

.section-cards {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.section-card {
    display: flex;
    align-items: center;
    gap: 1.25rem;
    background: var(--bg-card);
    border-radius: var(--border-radius);
    padding: 1.25rem 1.5rem;
    border: 1px solid rgba(255, 255, 255, 0.05);
    transition: all var(--transition-normal);
}

.section-card:hover {
    background: var(--bg-tertiary);
    border-color: rgba(99, 102, 241, 0.3);
    transform: translateX(8px);
}

.section-number {
    width: 48px;
    height: 48px;
    background: var(--accent-gradient);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.25rem;
    font-weight: 700;
    flex-shrink: 0;
}

.section-info {
    flex: 1;
}

.section-info h3 {
    font-size: 1rem;
    margin-bottom: 0.25rem;
}

.section-info p {
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.section-arrow {
    font-size: 1.25rem;
    color: var(--text-muted);
    transition: transform var(--transition-fast);
}

.section-card:hover .section-arrow {
    transform: translateX(4px);
    color: var(--accent-secondary);
}

.start-prompt {
    text-align: center;
    margin-top: 3rem;
    padding: 1.5rem;
    background: rgba(99, 102, 241, 0.1);
    border-radius: var(--border-radius);
    color: var(--text-secondary);
}

/* ============================================
   Section Page (Страница секции)
   ============================================ */
.section-page {
    padding: 1rem 0;
}

.section-header {
    text-align: center;
    margin-bottom: 2.5rem;
}

.section-badge {
    display: inline-block;
    background: var(--accent-gradient);
    padding: 0.375rem 1rem;
    border-radius: 20px;
    font-size: 0.875rem;
    font-weight: 600;
    margin-bottom: 1rem;
}

.section-badge.small {
    font-size: 0.75rem;
    padding: 0.25rem 0.75rem;
}

.section-title {
    font-size: 2rem;
    font-weight: 700;
    margin-bottom: 0.75rem;
}

.section-description {
    color: var(--text-secondary);
    font-size: 1.125rem;
}

.levels-grid h2 {
    font-size: 1.25rem;
    margin-bottom: 1.25rem;
}

.levels-container {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
    gap: 1rem;
    margin-bottom: 2.5rem;
}

.level-card {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    background: var(--bg-card);
    border-radius: var(--border-radius);
    padding: 1.25rem;
    border: 1px solid rgba(255, 255, 255, 0.05);
    transition: all var(--transition-normal);
}

.level-card:hover {
    background: var(--bg-tertiary);
    border-color: rgba(99, 102, 241, 0.4);
    transform: translateY(-4px);
    box-shadow: var(--shadow-glow);
}

.level-number {
    font-size: 1.75rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
}

.level-difficulty {
    font-size: 0.75rem;
    color: var(--text-muted);
}

.section-tips {
    background: var(--bg-card);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    border: 1px solid rgba(255, 255, 255, 0.05);
}

.section-tips h3 {
    font-size: 1rem;
    margin-bottom: 1rem;
}

.section-tips ul {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.section-tips li {
    padding-left: 1.5rem;
    position: relative;
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.section-tips li::before {
    content: "•";
    position: absolute;
    left: 0;
    color: var(--accent-primary);
}

/* ============================================
   Level Page (Страница уровня)
   ============================================ */
.level-page {
    padding: 1rem 0;
}

.level-header {
    display: flex;
    flex-direction: column;
    gap: 1rem;
    margin-bottom: 2rem;
}

.back-link {
    color: var(--text-secondary);
    font-size: 0.875rem;
    transition: color var(--transition-fast);
}

.back-link:hover {
    color: var(--accent-secondary);
}

.level-info {
    display: flex;
    align-items: center;
    gap: 1rem;
}

.level-info h1 {
    font-size: 1.75rem;
}

.equation-card {
    background: var(--bg-card);
    border-radius: var(--border-radius);
    padding: 2.5rem;
    margin-bottom: 2rem;
    text-align: center;
    border: 1px solid rgba(255, 255, 255, 0.05);
    box-shadow: var(--shadow-md);
}

.equation-label {
    color: var(--text-secondary);
    font-size: 0.875rem;
    margin-bottom: 1.5rem;
}

.equation-display {
    font-size: 1.75rem;
    min-height: 60px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.answer-section {
    background: var(--bg-card);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    margin-bottom: 2rem;
    border: 1px solid rgba(255, 255, 255, 0.05);
}

.answer-form {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.answer-label {
    font-size: 0.9rem;
    color: var(--text-secondary);
}

.answer-input-group {
    display: flex;
    gap: 1rem;
}

.answer-input {
    flex: 1;
    background: var(--bg-tertiary);
    border: 2px solid rgba(255, 255, 255, 0.1);
    border-radius: var(--border-radius-sm);
    padding: 0.875rem 1rem;
    font-size: 1.125rem;
    color: var(--text-primary);
    transition: all var(--transition-fast);
}

.answer-input:focus {
    outline: none;
    border-color: var(--accent-primary);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.2);
}

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

.submit-btn {
    background: var(--accent-gradient);
    color: white;
    font-weight: 600;
    padding: 0.875rem 2rem;
    border-radius: var(--border-radius-sm);
    transition: all var(--transition-fast);
}

.submit-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-glow);
}

.result-message {
    display: flex;
    align-items: center;
    gap: 1rem;
    padding: 1rem;
    border-radius: var(--border-radius-sm);
    margin-top: 1rem;
    animation: slideIn 0.3s ease;
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateY(-10px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.result-message.success {
    background: var(--success-bg);
    border: 1px solid var(--success);
}

.result-message.error {
    background: var(--error-bg);
    border: 1px solid var(--error);
}

.result-icon {
    font-size: 1.5rem;
}

.result-text {
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
}

.result-text strong {
    font-size: 1rem;
}

.result-text span {
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.level-actions {
    display: flex;
    gap: 1rem;
    justify-content: center;
    flex-wrap: wrap;
}

.new-equation-btn,
.next-level-btn {
    padding: 0.75rem 1.5rem;
    border-radius: var(--border-radius-sm);
    font-weight: 500;
    transition: all var(--transition-fast);
}

.new-equation-btn {
    background: var(--bg-tertiary);
    color: var(--text-primary);
    border: 1px solid rgba(255, 255, 255, 0.1);
}

.new-equation-btn:hover {
    background: var(--bg-card);
    border-color: rgba(255, 255, 255, 0.2);
}

.next-level-btn {
    background: var(--accent-gradient);
    color: white;
}

.next-level-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-glow);
}

/* Decimal Toggle */
.decimal-toggle {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.5rem 1rem;
    background: var(--bg-tertiary);
    border-radius: var(--border-radius-sm);
    border: 1px solid rgba(255, 255, 255, 0.1);
    cursor: pointer;
    font-size: 0.875rem;
    color: var(--text-secondary);
    transition: all var(--transition-fast);
}

.decimal-toggle:hover {
    border-color: rgba(99, 102, 241, 0.4);
    color: var(--text-primary);
}

.decimal-toggle input[type="checkbox"] {
    width: 18px;
    height: 18px;
    accent-color: var(--accent-primary);
    cursor: pointer;
}

.decimal-toggle span {
    white-space: nowrap;
}

.grade-warning {
    color: #f39c12;
    font-size: 0.75rem;
    font-style: italic;
    margin-left: 0.5rem;
}

/* ============================================
   HTMX Transitions
   ============================================ */
.htmx-swapping {
    opacity: 0.5;
    transition: opacity var(--transition-fast);
}

.htmx-settling {
    opacity: 1;
}

/* ============================================
   Burger Menu (мобильные)
   ============================================ */
.burger-btn {
    display: none;
    position: fixed;
    top: 1rem;
    left: 1rem;
    z-index: 200;
    width: 44px;
    height: 44px;
    border-radius: var(--border-radius-sm);
    background: var(--bg-secondary);
    border: 1px solid rgba(255, 255, 255, 0.1);
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 5px;
    cursor: pointer;
    transition: all var(--transition-fast);
    box-shadow: var(--shadow-sm);
}

.burger-btn:hover {
    background: var(--bg-tertiary);
    border-color: rgba(99, 102, 241, 0.4);
}

.burger-line {
    display: block;
    width: 20px;
    height: 2px;
    background: var(--text-primary);
    border-radius: 1px;
    transition: all var(--transition-fast);
}

.burger-btn.active .burger-line:nth-child(1) {
    transform: rotate(45deg) translate(5px, 5px);
}

.burger-btn.active .burger-line:nth-child(2) {
    opacity: 0;
}

.burger-btn.active .burger-line:nth-child(3) {
    transform: rotate(-45deg) translate(5px, -5px);
}

.sidebar-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.6);
    z-index: 90;
    opacity: 0;
    pointer-events: none;
    transition: opacity var(--transition-normal);
    backdrop-filter: blur(2px);
}

.sidebar-overlay.visible {
    opacity: 1;
    pointer-events: auto;
}

/* ============================================
   Index: Level Cards (Главная страница)
   ============================================ */
.levels-overview h2 {
    font-size: 1.5rem;
    margin-bottom: 1.5rem;
}

.level-cards {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.level-cards .level-card {
    display: flex;
    align-items: center;
    gap: 1.25rem;
    padding: 1.25rem 1.5rem;
    flex-direction: row;
    justify-content: flex-start;
    text-align: left;
}

.level-cards .level-card .level-number {
    width: 52px;
    height: 52px;
    min-width: 52px;
    background: var(--accent-gradient);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.25rem;
    font-weight: 700;
    margin-bottom: 0;
}

.level-cards .level-card .level-info {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
}

.level-cards .level-card .level-info h3 {
    font-size: 1.0625rem;
    font-weight: 600;
}

.level-cards .level-card .level-info p {
    font-size: 0.875rem;
    color: var(--text-secondary);
    line-height: 1.4;
}

.level-types-count {
    font-size: 0.75rem;
    color: var(--text-muted);
    font-weight: 500;
}

.level-arrow {
    font-size: 1.25rem;
    color: var(--text-muted);
    transition: transform var(--transition-fast);
    flex-shrink: 0;
}

.level-cards .level-card:hover .level-arrow {
    transform: translateX(4px);
    color: var(--accent-secondary);
}

.level-cards .level-card:hover {
    transform: translateX(6px);
}

/* ============================================
   Level Page (Страница уровня)
   ============================================ */
.level-badge {
    display: inline-block;
    background: var(--accent-gradient);
    padding: 0.375rem 1rem;
    border-radius: 20px;
    font-size: 0.875rem;
    font-weight: 600;
    margin-bottom: 0.75rem;
}

.level-badge.small {
    font-size: 0.75rem;
    padding: 0.25rem 0.75rem;
}

.level-title {
    font-size: 2rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
}

.level-description {
    color: var(--text-secondary);
    font-size: 1rem;
    line-height: 1.5;
}

/* Mix секция */
.mix-section {
    margin-bottom: 2rem;
}

.mix-card {
    display: flex;
    align-items: center;
    gap: 1.25rem;
    background: linear-gradient(135deg, rgba(99, 102, 241, 0.15) 0%, rgba(168, 85, 247, 0.15) 100%);
    border: 1px solid rgba(99, 102, 241, 0.3);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    transition: all var(--transition-normal);
}

.mix-card:hover {
    border-color: rgba(99, 102, 241, 0.6);
    transform: translateY(-2px);
    box-shadow: var(--shadow-glow);
}

.mix-icon {
    font-size: 2.5rem;
    flex-shrink: 0;
}

.mix-info {
    flex: 1;
}

.mix-info h2 {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: 0.25rem;
}

.mix-info p {
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.mix-arrow {
    font-size: 1.5rem;
    color: var(--text-muted);
    transition: transform var(--transition-fast);
    flex-shrink: 0;
}

.mix-card:hover .mix-arrow {
    transform: translateX(4px);
    color: var(--accent-secondary);
}

/* Типы уравнений */
.types-section {
    margin-bottom: 2rem;
}

.types-section h2 {
    font-size: 1.25rem;
    margin-bottom: 1.25rem;
}

.types-grid {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.type-card {
    display: flex;
    align-items: flex-start;
    gap: 1rem;
    background: var(--bg-card);
    border-radius: var(--border-radius);
    padding: 1.25rem 1.5rem;
    border: 1px solid rgba(255, 255, 255, 0.05);
    transition: all var(--transition-normal);
}

.type-card:hover {
    background: var(--bg-tertiary);
    border-color: rgba(99, 102, 241, 0.3);
    transform: translateX(4px);
}

.type-number {
    width: 40px;
    height: 40px;
    min-width: 40px;
    background: var(--bg-tertiary);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.875rem;
    font-weight: 700;
    color: var(--accent-secondary);
    border: 1px solid rgba(99, 102, 241, 0.2);
}

.type-info {
    flex: 1;
    min-width: 0;
}

.type-info h3 {
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: 0.25rem;
}

.type-template {
    font-size: 0.9375rem;
    color: var(--text-secondary);
    margin-bottom: 0.25rem;
}

.type-description {
    font-size: 0.8125rem;
    color: var(--text-muted);
    line-height: 1.4;
}

/* Навигация по уровням */
.level-navigation {
    display: flex;
    justify-content: space-between;
    gap: 1rem;
    margin-top: 2rem;
    padding-top: 1.5rem;
    border-top: 1px solid rgba(255, 255, 255, 0.05);
}

.nav-btn {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.75rem 1.5rem;
    background: var(--bg-card);
    border: 1px solid rgba(255, 255, 255, 0.1);
    border-radius: var(--border-radius-sm);
    color: var(--text-secondary);
    font-weight: 500;
    transition: all var(--transition-fast);
}

.nav-btn:hover {
    background: var(--bg-tertiary);
    border-color: rgba(99, 102, 241, 0.4);
    color: var(--text-primary);
}

.nav-btn.next {
    margin-left: auto;
}

/* ============================================
   Trainer Page (Тренажёр)
   ============================================ */
.trainer-page {
    padding: 1rem 0;
}

.trainer-header {
    display: flex;
    flex-direction: column;
    gap: 1rem;
    margin-bottom: 2rem;
}

.trainer-info {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.trainer-info h1 {
    font-size: 1.75rem;
    font-weight: 700;
}

.type-template-display {
    font-size: 1.125rem;
    color: var(--text-secondary);
}

.equation-type-hint {
    color: var(--text-muted);
    font-size: 0.875rem;
    margin-top: 0.75rem;
}

.trainer-actions {
    display: flex;
    gap: 1rem;
    justify-content: center;
    flex-wrap: wrap;
    margin-bottom: 2rem;
}

.mix-btn {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.75rem 1.5rem;
    border-radius: var(--border-radius-sm);
    font-weight: 500;
    background: linear-gradient(135deg, rgba(99, 102, 241, 0.15) 0%, rgba(168, 85, 247, 0.15) 100%);
    border: 1px solid rgba(99, 102, 241, 0.3);
    color: var(--text-primary);
    transition: all var(--transition-fast);
}

.mix-btn:hover {
    border-color: rgba(99, 102, 241, 0.6);
    transform: translateY(-2px);
    box-shadow: var(--shadow-glow);
}

/* Советы по решению */
.solving-tips {
    background: var(--bg-card);
    border-radius: var(--border-radius);
    padding: 1.5rem;
    border: 1px solid rgba(255, 255, 255, 0.05);
    margin-top: 1rem;
}

.solving-tips h2 {
    font-size: 1.125rem;
    margin-bottom: 0.75rem;
}

.solving-tips p {
    color: var(--text-secondary);
    font-size: 0.9375rem;
    line-height: 1.6;
}

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

/* Планшеты */
@media (max-width: 1024px) {
    :root {
        --sidebar-width: 250px;
    }

    .main-content {
        padding: 1.5rem;
    }

    .welcome-title {
        font-size: 2rem;
    }

    .equation-card {
        padding: 2rem;
    }
}

/* Мобильные */
@media (max-width: 768px) {
    .burger-btn {
        display: flex;
    }

    .sidebar-overlay {
        display: block;
    }

    .sidebar {
        transform: translateX(-100%);
        transition: transform var(--transition-normal);
        width: 280px;
    }

    .sidebar.open {
        transform: translateX(0);
    }

    .main-content {
        margin-left: 0;
        padding: 1rem;
        padding-top: 4rem;
    }

    .welcome-title {
        font-size: 1.75rem;
    }

    .mobile-cta-btn {
        display: inline-block;
    }

    .equation-display {
        font-size: 1.25rem;
    }

    .answer-input-group {
        flex-direction: column;
    }

    .levels-container {
        grid-template-columns: repeat(3, 1fr);
    }

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

    .mix-card {
        padding: 1.25rem;
    }

    .level-navigation {
        flex-direction: column;
    }

    .nav-btn.next {
        margin-left: 0;
    }

    .trainer-info h1 {
        font-size: 1.5rem;
    }

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

/* Маленькие телефоны */
@media (max-width: 480px) {
    .main-content {
        padding: 0.75rem;
        padding-top: 4rem;
    }

    .levels-container {
        grid-template-columns: repeat(2, 1fr);
    }

    .level-cards .level-card {
        padding: 1rem;
        gap: 1rem;
    }

    .level-cards .level-card .level-number {
        width: 44px;
        height: 44px;
        min-width: 44px;
        font-size: 1.125rem;
    }

    .type-card {
        padding: 1rem;
    }

    .equation-card {
        padding: 1.5rem;
    }

    .answer-input {
        font-size: 1rem;
        padding: 0.75rem;
    }

    .submit-btn {
        padding: 0.75rem 1.5rem;
    }

    .trainer-actions {
        flex-direction: column;
    }

    .trainer-actions .new-equation-btn,
    .trainer-actions .next-level-btn,
    .trainer-actions .mix-btn {
        width: 100%;
        justify-content: center;
    }

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

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

/* ============================================
   Scrollbar Styling
   ============================================ */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: var(--bg-primary);
}

::-webkit-scrollbar-thumb {
    background: var(--bg-tertiary);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--accent-primary);
}

/* ============================================
   Error Pages (404, 500)
   ============================================ */
.error-page {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    text-align: center;
    padding: 4rem 1rem;
    min-height: 60vh;
}

.error-icon {
    font-size: 4rem;
    margin-bottom: 1rem;
    animation: float 3s ease-in-out infinite;
}

@keyframes float {

    0%,
    100% {
        transform: translateY(0);
    }

    50% {
        transform: translateY(-10px);
    }
}

.error-code {
    font-size: 6rem;
    font-weight: 800;
    line-height: 1;
    margin-bottom: 0.5rem;
    background: var(--accent-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.error-title {
    font-size: 1.5rem;
    font-weight: 600;
    margin-bottom: 1rem;
    color: var(--text-primary);
}

.error-description {
    font-size: 1.125rem;
    color: var(--text-secondary);
    max-width: 500px;
    margin-bottom: 2rem;
    line-height: 1.6;
}

.error-actions {
    display: flex;
    gap: 1rem;
    flex-wrap: wrap;
    justify-content: center;
}

.error-btn {
    padding: 0.875rem 2rem;
    border-radius: var(--border-radius-sm);
    font-weight: 500;
    transition: all var(--transition-fast);
    text-decoration: none;
    cursor: pointer;
    font-size: 1rem;
    border: none;
    outline: none;
}

.error-btn.primary {
    background: var(--accent-gradient);
    color: white;
}

.error-btn.primary:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-glow);
}

.error-btn.secondary {
    background: var(--bg-tertiary);
    color: var(--text-primary);
    border: 1px solid rgba(255, 255, 255, 0.1);
}

.error-btn.secondary:hover {
    background: var(--bg-card);
    border-color: rgba(255, 255, 255, 0.2);
    transform: translateY(-2px);
}