:root {
    --bg-color: #F8FAFC;
    --card-bg: #FFFFFF;
    --text-main: #0F172A;
    --text-muted: #64748B;
    --algebra-color: #2563EB;
    --algebra-bg: #DBEAFE;
    --geometry-color: #059669;
    --geometry-bg: #D1FAE5;
    --border-color: #E2E8F0;
    --border-radius: 12px;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
}

body {
    background-color: var(--bg-color);
    color: var(--text-main);
    line-height: 1.5;
}

/* --- ШАПКА НА ВСЮ ШИРИНУ --- */
.header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 16px 32px;
    background: #ffffff;
    border-bottom: 1px solid var(--border-color);
    width: 100%;
}

.logo {
    font-size: 1.6rem;
    font-weight: 800;
    color: var(--text-main);
    text-decoration: none;
    letter-spacing: -0.5px;
}

.logo span {
    color: var(--algebra-color);
}

.header-actions {
    display: flex;
    gap: 12px;
    align-items: center;
}

/* Кнопки и выпадающий список в шапке */
.btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 10px 18px;
    font-size: 0.9rem;
    font-weight: 600;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s ease;
    border: 1px solid transparent;
}

.btn-primary {
    background: var(--algebra-color);
    color: white;
}

.btn-primary:hover {
    background: #1D4ED8;
}

.lang-select-wrapper {
    position: relative;
    display: inline-block;
}

.lang-select {
    appearance: none;
    background-color: white;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 8px 30px 8px 12px;
    font-size: 0.9rem;
    font-weight: 700;
    color: var(--text-main);
    cursor: pointer;
    outline: none;
    background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='14' height='14' viewBox='0 0 24 24' fill='none' stroke='%2364748B' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'><polyline points='6 9 12 15 18 9'></polyline></svg>");
    background-repeat: no-repeat;
    background-position: right 10px center;
}

/* --- ЛЕЙАУТ ПРИЛОЖЕНИЯ (РАСТЯНУТ ДО КРАЕВ) --- */
.app-container {
    display: flex;
    gap: 32px;
    width: 100%;
    padding: 24px 32px; /* Паддинги от краев экрана */
    align-items: flex-start;
}

/* --- САЙДБАР СЛЕВА --- */
.sidebar {
    width: 250px;
    flex-shrink: 0;
    background: #ffffff;
    border-radius: 16px;
    padding: 20px;
    border: 1px solid var(--border-color);
    position: sticky;
    top: 24px;
    box-shadow: 0 1px 3px rgba(0,0,0,0.02);
}

.sidebar h3 {
    font-size: 1.1rem;
    margin-bottom: 16px;
    color: var(--text-main);
}

.topic-list {
    list-style: none;
}

.topic-item {
    padding: 10px 14px;
    border-radius: 10px;
    cursor: pointer;
    font-size: 0.95rem;
    color: var(--text-muted);
    margin-bottom: 4px;
    transition: all 0.2s ease;
}

.topic-item:hover {
    background: #F1F5F9;
    color: var(--text-main);
}

.topic-item.active {
    background: var(--algebra-color);
    color: #ffffff;
    font-weight: 600;
}

/* --- ПРАВАЯ ОБЛАСТЬ С КОНТЕНТОМ --- */
.main-content {
    flex-grow: 1;
    display: flex;
    flex-direction: column;
    align-items: center; /* Центрируем заголовки, поиск и кнопки по центру правой области */
    min-width: 0;
}

.hero {
    text-align: center;
    margin-bottom: 24px;
}

.hero h1 {
    font-size: 2.2rem;
    font-weight: 800;
    margin-bottom: 8px;
    letter-spacing: -0.5px;
}

.hero p {
    color: var(--text-muted);
    font-size: 1.05rem;
}

/* Поиск */
.search-box {
    width: 100%;
    max-width: 720px;
    margin-bottom: 24px;
}

.search-input {
    width: 100%;
    padding: 16px 20px;
    font-size: 1.05rem;
    border: 2px solid var(--border-color);
    border-radius: var(--border-radius);
    outline: none;
    background: white;
    transition: all 0.2s ease-in-out;
    box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.04);
}

.search-input:focus {
    border-color: var(--algebra-color);
    box-shadow: 0 10px 15px -3px rgba(37, 99, 235, 0.12);
}

/* Фильтры */
.filters {
    display: flex;
    flex-direction: column;
    gap: 16px;
    align-items: center;
    margin-bottom: 28px;
    width: 100%;
}

.view-toggle, .subject-toggle {
    display: flex;
    gap: 4px;
    background: #E2E8F0;
    padding: 4px;
    border-radius: 10px;
}

.view-btn, .subject-btn {
    padding: 8px 18px;
    border: none;
    background: transparent;
    font-weight: 700;
    font-size: 0.9rem;
    cursor: pointer;
    border-radius: 8px;
    transition: all 0.2s ease;
    color: var(--text-muted);
}

.view-btn.active, .subject-btn.active-all {
    background: white;
    color: var(--text-main);
    box-shadow: 0 1px 3px rgba(0,0,0,0.1);
}

.subject-btn.active-algebra {
    background: var(--algebra-color);
    color: white;
}

.subject-btn.active-geometry {
    background: var(--geometry-color);
    color: white;
}

.class-selector {
    display: flex;
    gap: 8px;
    flex-wrap: wrap;
    justify-content: center;
}

.class-chip {
    padding: 6px 16px;
    border: 1px solid #CBD5E1;
    background: white;
    border-radius: 20px;
    cursor: pointer;
    font-weight: 600;
    font-size: 0.88rem;
    color: var(--text-muted);
    transition: all 0.2s ease;
}

.class-chip:hover,
.class-chip.active {
    background: var(--text-main);
    color: white;
    border-color: var(--text-main);
}

/* --- СЕТКА КАРТОЧЕК --- */
.grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 20px;
    width: 100%;
}

.card {
    position: relative;
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    padding: 20px;
    box-shadow: 0 1px 3px rgba(0,0,0,0.05);
    cursor: pointer;
    transition: box-shadow 0.2s ease, border-color 0.2s ease;
}

.card:hover {
    border-color: var(--algebra-color);
    box-shadow: 0 4px 10px rgba(0,0,0,0.08);
}

.card-hint {
    font-size: 0.8rem;
    color: var(--text-muted);
    margin-top: 10px;
}

.card-details {
    display: none;
    cursor: default;
}

.card.expanded .card-hint {
    display: none;
}

.card.expanded .card-details {
    display: block;
}

.card p {
    text-align: center !important;
    display: flex !important;
    justify-content: center !important;
    align-items: center !important;
    width: 100% !important;
    margin-top: 12px;
}

.card mjx-container {
    margin: 0 auto !important;
    text-align: center !important;
}

.fav-btn {
    position: absolute;
    top: 16px;
    right: 16px;
    background: none;
    border: none;
    font-size: 1.4rem;
    cursor: pointer;
    color: #CBD5E1;
    transition: color 0.2s, transform 0.1s;
    line-height: 1;
    padding: 0;
}

.fav-btn:hover {
    transform: scale(1.15);
}

.fav-btn.active {
    color: #F59E0B;
}

/* --- ПЕЧАТЬ (ШПАРГАЛКА) --- */
/*Стало:*/
@media print {
    .header, .sidebar, .hero, .search-box, .filters, .fav-btn, .calculator-box, .card-hint {
        display: none !important;
    }

    .card-details {
        display: block !important;
    }

    body {
        background: white !important;
        color: black !important;
        padding: 0;
        margin: 0;
    }

    .app-container {
        display: block !important;
        padding: 0 !important;
    }

    .main-content {
        width: 100% !important;
    }

    .grid {
        display: grid !important;
        grid-template-columns: repeat(3, 1fr) !important;
        gap: 8px !important;
    }

    .card {
        border: 1px solid #000 !important;
        box-shadow: none !important;
        padding: 6px 10px !important;
        page-break-inside: avoid;
        border-radius: 4px !important;
    }
}
.details-card {
    background: #ffffff;
    padding: 24px;
    border-radius: 12px;
    border: 1px solid #E2E8F0;
}
.calculator-box {
    margin-top: 20px;
    background: #F8FAFC;
    padding: 16px;
    border-radius: 8px;
}
.formula-legend {
    margin-top: 12px;
    padding: 12px 14px;
    background: #F1F5F9;
    border-left: 3px solid var(--algebra-color);
    border-radius: 6px;
    font-size: 0.85rem;
    color: #475569;
}
.formula-legend strong {
    display: block;
    margin-bottom: 6px;
    color: var(--text-main);
    font-size: 0.85rem;
}
.formula-legend ul {
    list-style: none;
    margin: 0;
    padding: 0;
    display: flex;
    flex-wrap: wrap;
    gap: 6px 16px;
}
.formula-legend li {
    white-space: nowrap;
}
.calc-input {
    width: 100%;
    padding: 8px 12px;
    margin: 6px 0 12px 0;
    border: 1px solid #CBD5E1;
    border-radius: 6px;
    box-sizing: border-box;
}

/* --- ПУСТОЕ СОСТОЯНИЕ (ничего не выбрано) --- */
.empty-state {
    grid-column: 1 / -1;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    text-align: center;
    padding: 80px 24px;
    color: var(--text-muted);
    background: var(--card-bg);
    border: 1px dashed var(--border-color);
    border-radius: var(--border-radius);
}

.empty-state-icon {
    font-size: 2.5rem;
    margin-bottom: 12px;
}

.empty-state h3 {
    font-size: 1.25rem;
    color: var(--text-main);
    margin-bottom: 8px;
}

.empty-state p {
    font-size: 0.95rem;
    max-width: 360px;
}