:root {
  --bg: #f1f4fa;
  --header-bg: #0f1b2d;
  --header-accent: #2952a3;
  --accent: #2952a3;
  --accent-dark: #16213e;
  --card-bg: #ffffff;
  --card-border: #e3e7f0;
  --muted: #667085;
  --badge-bg: #fbe8c6;
  --badge-text: #7a4b00;
  --serif: Georgia, "Iowan Old Style", "Palatino Linotype", "Times New Roman", serif;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  font-family: var(--sans);
  background: var(--bg);
  color: #1a2233;
}

h1, h2, h3 {
  font-family: var(--serif);
  color: var(--accent-dark);
}

p {
  font-size: 17px;
  line-height: 1.65;
  color: #2c3547;
}

ul {
  padding-left: 22px;
  line-height: 1.8;
}

a {
  color: var(--accent);
}

/* ---------- Шапка сайта (nav.js) ---------- */

header {
  background: var(--header-bg);
  padding: 0 28px;
  border-bottom: 3px solid var(--header-accent);
}

.top-menu {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  align-items: center;
  flex-wrap: wrap;
}

.top-menu li {
  position: relative;
}

.top-menu a {
  display: block;
  color: #e8ecf5;
  text-decoration: none;
  padding: 20px 16px;
  font-size: 15px;
  letter-spacing: 0.01em;
  transition: color 0.15s, background 0.15s;
}

.top-menu a:hover {
  color: #ffffff;
  background: rgba(255, 255, 255, 0.08);
}

.site-logo a {
  padding: 10px 14px;
  display: flex;
  align-items: center;
}

.site-logo img {
  height: 28px;
  width: auto;
  display: block;
}

.dropdown-menu {
  display: none;
  position: absolute;
  top: 100%;
  left: 0;
  min-width: 270px;
  background: var(--card-bg);
  box-shadow: 0 14px 32px rgba(15, 27, 45, 0.18);
  border-radius: 12px;
  overflow: hidden;
  z-index: 10;
  padding: 6px;
}

.dropdown-menu a {
  color: #1a2233;
  background: transparent;
  padding: 12px 14px;
  border-radius: 8px;
}

.dropdown-menu a:hover {
  background: #eef2fb;
  color: var(--accent);
}

.dropdown:hover .dropdown-menu,
.dropdown:focus-within .dropdown-menu {
  display: block;
}

/* ---------- Простые страницы (index/news/other) ---------- */

main {
  width: 100%;
  max-width: 880px;
  margin: 48px auto;
  background: var(--card-bg);
  padding: 40px 44px;
  border-radius: 18px;
  border: 1px solid var(--card-border);
  box-shadow: 0 14px 34px rgba(15, 27, 45, 0.06);
}

main h1 {
  margin-top: 0;
  margin-bottom: 16px;
  font-size: 34px;
}

main h2 {
  margin-top: 30px;
  margin-bottom: 14px;
  font-size: 22px;
}

.back-link {
  display: inline-block;
  margin-top: 24px;
  color: var(--accent);
  text-decoration: none;
  font-weight: bold;
}

.back-link:hover {
  text-decoration: underline;
}

/* ---------- Предметная страница (subject.html) ---------- */

.subject-page {
  max-width: 980px;
  margin: 0 auto;
  padding: 48px 20px 80px;
}

.subject-topbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 20px;
  flex-wrap: wrap;
  margin-bottom: 30px;
}

.subject-topbar h1 {
  font-size: 40px;
  margin: 0;
}

.language-switcher {
  display: flex;
  gap: 6px;
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: 999px;
  padding: 4px;
}

.lang-btn {
  padding: 7px 16px;
  border: none;
  background: transparent;
  cursor: pointer;
  border-radius: 999px;
  font-family: var(--sans);
  font-size: 14px;
  color: var(--muted);
  transition: background 0.15s, color 0.15s;
}

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

.lang-btn.active {
  background: var(--accent-dark);
  color: #fff;
}

.topics-accordion {
  display: flex;
  flex-direction: column;
  gap: 18px;
  counter-reset: topic-counter;
}

.empty-state,
.subtopic-loading {
  color: var(--muted);
  font-style: italic;
  padding: 4px 0;
}

/* Тема (уровень 1): "Множества", "Тригонометрия" ... */

.topic-block {
  counter-increment: topic-counter;
  border: 1px solid var(--card-border);
  border-radius: 16px;
  background: var(--card-bg);
  overflow: hidden;
  box-shadow: 0 6px 18px rgba(15, 27, 45, 0.05);
}

.topic-block > summary {
  padding: 22px 26px;
  font-family: var(--serif);
  font-size: 23px;
  font-weight: 700;
  cursor: pointer;
  list-style: none;
  color: var(--accent-dark);
  transition: background 0.15s;
}

.topic-block > summary::before {
  content: counter(topic-counter) ". ";
  color: var(--accent);
}

.topic-block > summary:hover {
  background: #f7f9fd;
}

.topic-block > summary::-webkit-details-marker {
  display: none;
}

.topic-block[open] > summary {
  border-bottom: 1px solid var(--card-border);
}

.topic-body {
  counter-reset: subtopic-counter;
  padding: 16px;
  background: #fafbfe;
  display: flex;
  flex-direction: column;
  gap: 12px;
}

/* Подтема (уровень 2): "Отношения между множествами" ... */

.subtopic-block {
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: 12px;
  overflow: hidden;
}

.subtopic-block > summary {
  padding: 14px 18px;
  font-size: 17px;
  font-weight: 600;
  cursor: pointer;
  list-style: none;
  border-left: 5px solid var(--accent);
  transition: background 0.15s;
}

.subtopic-block {
  counter-increment: subtopic-counter;
}

.subtopic-block > summary::before {
  content: counter(topic-counter) "." counter(subtopic-counter);
  display: inline-block;
  min-width: 36px;
  margin-right: 8px;
  color: var(--accent);
  font-weight: 700;
}

.subtopic-block > summary:hover {
  background: #f7f9fd;
}

.subtopic-block > summary::-webkit-details-marker {
  display: none;
}

.subtopic-body {
  padding: 20px 22px;
  background: #fdfdff;
  border-top: 1px solid #eef1f5;
}

.subtopic-intro {
  margin: 0 0 14px;
  color: var(--muted);
  line-height: 1.6;
}

/* Список заданий внутри подтемы */

.tasks-list {
  display: flex;
  flex-direction: column;
  gap: 22px;
}

.task-item {
  padding-top: 20px;
  border-top: 1px solid #eef1f5;
}

.tasks-list .task-item:first-child {
  padding-top: 0;
  border-top: none;
}

.task-head {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 10px;
}

.task-number {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 26px;
  height: 26px;
  padding: 0 6px;
  border-radius: 999px;
  background: var(--accent-dark);
  color: #fff;
  font-size: 13px;
  font-weight: 700;
}

.task-badge {
  display: inline-block;
  padding: 3px 12px;
  font-size: 13px;
  font-weight: 600;
  color: var(--badge-text);
  background: var(--badge-bg);
  border-radius: 999px;
}

.task-question {
  margin: 0 0 14px;
  font-size: 18px;
  line-height: 1.55;
  color: #1a2233;
}

.task-options {
  list-style: none;
  padding: 0;
  margin: 0 0 14px;
}

.task-options li {
  margin-bottom: 8px;
  line-height: 1.6;
}

.task-explanation {
  margin-top: 12px;
}

.task-explanation summary {
  cursor: pointer;
  display: inline-block;
  color: var(--accent);
  font-weight: 600;
  font-size: 14px;
  padding: 7px 14px;
  border: 1px solid var(--accent);
  border-radius: 999px;
  list-style: none;
  transition: background 0.15s, color 0.15s;
}

.task-explanation summary::-webkit-details-marker {
  display: none;
}

.task-explanation summary:hover {
  background: var(--accent);
  color: #fff;
}

.explanation-content {
  margin-top: 14px;
  padding: 16px 20px;
  background: #f5f7fb;
  border-radius: 10px;
  line-height: 1.7;
}

/* ---------- Архив прошлых экзаменов (past-exams.html) ---------- */

.past-exams-page {
  max-width: 1000px;
  margin: 0 auto;
  padding: 48px 20px 80px;
}

.archive-intro {
  margin-bottom: 34px;
}

.archive-intro h1 {
  margin-bottom: 10px;
  font-size: 36px;
}

.archive-section {
  display: flex;
  flex-direction: column;
  gap: 24px;
}

.year-block {
  border: 1px solid var(--card-border);
  border-radius: 16px;
  background: var(--card-bg);
  overflow: hidden;
  box-shadow: 0 6px 18px rgba(15, 27, 45, 0.05);
}

.year-block > summary {
  display: flex;
  flex-direction: column;
  gap: 2px;
  padding: 22px 26px;
  cursor: pointer;
  list-style: none;
  border-bottom: 1px solid transparent;
}

.year-block[open] > summary {
  border-bottom: 1px solid var(--card-border);
}

.year-block > summary::-webkit-details-marker {
  display: none;
}

.year-title {
  font-family: var(--serif);
  font-size: 26px;
  font-weight: 700;
  color: var(--accent-dark);
}

.year-label {
  font-size: 13px;
  color: var(--muted);
  font-weight: 500;
}

.year-content {
  padding: 18px;
  background: #fafbfe;
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.month-block {
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: 12px;
  overflow: hidden;
}

.month-block > summary {
  padding: 14px 18px;
  font-size: 16px;
  font-weight: 600;
  cursor: pointer;
  list-style: none;
  border-left: 5px solid var(--accent);
}

.month-block > summary::-webkit-details-marker {
  display: none;
}

.month-content {
  padding: 18px;
  background: #fdfdff;
  border-top: 1px solid #eef1f5;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 16px;
}

.subject-card {
  background: #fafbfe;
  border: 1px solid var(--card-border);
  border-radius: 12px;
  padding: 16px 18px;
}

.subject-card h2 {
  margin: 0 0 12px;
  font-size: 17px;
  font-family: var(--sans);
  font-weight: 700;
  color: var(--accent-dark);
}

.file-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 10px;
  padding: 8px 0;
  border-top: 1px solid #eef1f5;
}

.file-row:first-of-type {
  border-top: none;
}

.file-row span {
  font-size: 14px;
  color: var(--muted);
}

.file-actions {
  display: flex;
  gap: 8px;
}

.file-actions a {
  font-size: 13px;
  font-weight: 600;
  text-decoration: none;
  color: var(--accent);
  padding: 5px 10px;
  border-radius: 999px;
  background: #eef2fb;
}

.file-actions a:hover {
  background: var(--accent);
  color: #fff;
}

@media (max-width: 640px) {
  main {
    width: auto;
    margin: 20px 12px;
    padding: 26px 22px;
  }

  .subject-topbar h1 {
    font-size: 30px;
  }

  .topic-block > summary {
    font-size: 19px;
    padding: 18px 20px;
  }

  .top-menu a {
    padding: 14px 12px;
    font-size: 14px;
  }
}

/* Картинки в условиях и решениях заданий: <img src="images/...."> */
.task-question img,
.task-options img,
.explanation-content img {
  max-width: 100%;
  height: auto;
  display: block;
  margin: 10px 0;
}

/* Группы внутри подтемы (например: формулы суммы / двойного / половинного угла) */
.group-block {
  background: #fff;
  border: 1px solid var(--card-border);
  border-radius: 10px;
  margin-bottom: 10px;
  overflow: hidden;
}

.group-block > summary {
  padding: 11px 16px;
  font-weight: 600;
  font-size: 15px;
  cursor: pointer;
  list-style: none;
  border-left: 4px solid #9fb4e0;
  transition: background 0.15s;
}

.group-block > summary::-webkit-details-marker {
  display: none;
}

.group-block > summary::before {
  content: "▸";
  display: inline-block;
  width: 16px;
  color: var(--accent);
  transition: transform 0.15s;
}

.group-block[open] > summary::before {
  transform: rotate(90deg);
}

.group-block > summary:hover {
  background: #f7f9fd;
}

.group-count {
  margin-left: 8px;
  padding: 1px 8px;
  font-size: 12px;
  font-weight: 600;
  color: var(--muted);
  background: #eef2fb;
  border-radius: 999px;
}

.group-body {
  padding: 16px 18px;
  border-top: 1px solid #eef1f5;
}

.task-appeared {
  font-size: 12px;
  color: var(--muted);
}


/* ---------- Поиск, отметка «решено», сквозная нумерация ---------- */
.search-box {
  margin-bottom: 18px;
}

.search-box input {
  width: 100%;
  padding: 13px 18px;
  font-size: 16px;
  font-family: var(--sans);
  border: 1px solid var(--card-border);
  border-radius: 12px;
  background: var(--card-bg);
  color: #1a2233;
}

.search-box input:focus {
  outline: 2px solid var(--accent);
  border-color: var(--accent);
}

.search-summary {
  color: var(--muted);
  font-size: 14px;
  margin: 0 0 12px;
}

.search-hit {
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: 12px;
  padding: 14px 18px 16px;
  margin-bottom: 12px;
}

.search-hit-head {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
  margin-bottom: 10px;
}

.search-hit-title {
  font-size: 13px;
  font-weight: 600;
  color: var(--muted);
}

.goto-btn {
  font-size: 13px;
  font-weight: 600;
  color: var(--accent);
  background: #eef2fb;
  border: none;
  border-radius: 999px;
  padding: 6px 12px;
  cursor: pointer;
}

.goto-btn:hover {
  background: var(--accent);
  color: #fff;
}

.search-hit .task-item {
  padding-top: 0;
  border-top: none;
}

.solved-btn {
  margin-left: auto;
  font-family: var(--sans);
  font-size: 13px;
  font-weight: 600;
  color: var(--muted);
  background: transparent;
  border: 1px solid var(--card-border);
  border-radius: 999px;
  padding: 4px 12px;
  cursor: pointer;
}

.solved-btn:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.solved-btn.on {
  color: #1b6b3a;
  background: #e5f5ea;
  border-color: #9fd3b0;
}

.task-item.is-solved .task-number {
  background: #2e8b57;
}

.task-item.flash {
  animation: task-flash 2.2s ease-out;
}

@keyframes task-flash {
  0%, 60% { background: #fff6d6; box-shadow: 0 0 0 8px #fff6d6; }
  100% { background: transparent; box-shadow: 0 0 0 8px transparent; }
}

.task-id {
  font-family: var(--sans);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.02em;
  color: #fff;
  background: var(--accent-dark);
  border: none;
  border-radius: 999px;
  padding: 4px 12px;
  cursor: pointer;
}

.task-id:hover {
  background: var(--accent);
}

.task-item.is-solved .task-id {
  background: #2e8b57;
}


/* ---------- Главная: ссылки-карточки ---------- */
.home-links {
  display: flex;
  gap: 16px;
  flex-wrap: wrap;
  margin-top: 24px;
}

.home-card {
  flex: 1 1 260px;
  display: flex;
  flex-direction: column;
  gap: 6px;
  padding: 20px 22px;
  background: #fff;
  border: 1px solid var(--card-border);
  border-left: 5px solid var(--accent);
  border-radius: 12px;
  text-decoration: none;
  color: inherit;
  transition: box-shadow 0.15s, transform 0.15s;
}

.home-card:hover {
  box-shadow: 0 6px 18px rgba(22, 33, 62, 0.12);
  transform: translateY(-2px);
}

.home-card-title {
  font-family: var(--serif);
  font-size: 22px;
  font-weight: 700;
  color: var(--accent-dark);
}

.home-card-text {
  font-size: 14px;
  color: var(--muted);
}

/* ---------- Новости: таблица расписания ---------- */
.news-meta {
  color: var(--muted);
  font-size: 14px;
}

.table-wrap {
  overflow-x: auto;
  margin: 18px 0;
}

.schedule-table {
  width: 100%;
  min-width: 560px;
  border-collapse: collapse;
  font-size: 15px;
  background: #fff;
}

.schedule-table th {
  background: var(--accent);
  color: #fff;
  padding: 10px 12px;
  text-align: center;
  font-weight: 600;
}

.schedule-table td {
  padding: 8px 12px;
  border: 1px solid #cdd5e6;
  text-align: center;
}

.schedule-table td.sess,
.schedule-table td.date {
  font-weight: 600;
}

.schedule-table tr.alt td {
  background: #e3f1fb;
}


.home-counter {
  margin: 22px 0 6px;
  padding: 12px 16px;
  background: #eef2fb;
  border-radius: 10px;
  font-size: 16px;
}

.home-list {
  line-height: 1.6;
}

.home-next {
  background: #fff;
  border: 1px solid var(--card-border);
  border-left: 5px solid var(--accent);
  border-radius: 12px;
  padding: 14px 20px;
}

.home-next p {
  margin: 0 0 6px;
  font-size: 17px;
}

.home-next a {
  font-weight: 600;
  color: var(--accent);
}

main a[href^="https://t.me"] {
  font-weight: 700;
}


/* ---------- Подвал ---------- */
.site-footer {
  margin-top: auto;
  background: var(--header-bg);
  color: #c9d3e6;
  border-top: 3px solid var(--header-accent);
}

.footer-inner {
  max-width: 980px;
  margin: 0 auto;
  padding: 32px 24px 22px;
  display: grid;
  grid-template-columns: 1.4fr 1fr 1.2fr;
  gap: 28px;
}

.footer-col {
  display: flex;
  flex-direction: column;
  gap: 8px;
  font-size: 14px;
  line-height: 1.5;
}

.footer-col p {
  margin: 0;
  color: #9fb0cc;
}

.footer-title {
  font-family: var(--serif);
  font-size: 17px;
  font-weight: 700;
  color: #fff;
  margin-bottom: 4px;
}

.footer-col a {
  color: #c9d3e6;
  text-decoration: none;
}

.footer-col a:hover {
  color: #fff;
  text-decoration: underline;
}

.footer-bottom {
  border-top: 1px solid rgba(255, 255, 255, 0.1);
  text-align: center;
  padding: 14px 24px;
  font-size: 13px;
  color: #8294b3;
}

@media (max-width: 640px) {
  .footer-inner {
    grid-template-columns: 1fr;
    gap: 20px;
    padding: 24px 20px 16px;
  }
}