:root {
  --bg: #f4f6fb;
  --surface: #ffffff;
  --surface-muted: #f8fafc;
  --border: #e2e8f0;
  --text: #0f172a;
  --text-muted: #475569;
  --text-soft: #64748b;
  --primary: #4f46e5;
  --primary-hover: #4338ca;
  --success: #059669;
  --success-bg: #ecfdf5;
  --success-border: #a7f3d0;
  --danger: #dc2626;
  --danger-hover: #b91c1c;
  --danger-bg: #fef2f2;
  --warn: #d97706;
  --warn-bg: #fffbeb;
  --radius: 14px;
  --shadow: 0 4px 20px rgba(15, 23, 42, 0.06);
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Inter, Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}

.hidden {
  display: none !important;
}

.container {
  max-width: 1020px;
  margin: 0 auto;
  padding: 0 16px;
}

/* Шапка */
.topbar {
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 20;
}

.topbar-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  height: 64px;
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
}

.brand-logo {
  width: 38px;
  height: 38px;
  border-radius: 10px;
  background: var(--primary);
  color: #fff;
  font-weight: 700;
  font-size: 20px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

.brand-title {
  font-weight: 700;
  font-size: 16px;
  line-height: 1.2;
}

.brand-subtitle {
  font-size: 12px;
  color: var(--text-soft);
}

.nav {
  display: flex;
  gap: 6px;
}

.nav-btn {
  border: 1px solid transparent;
  background: transparent;
  color: var(--text-muted);
  font-size: 14px;
  font-weight: 600;
  padding: 8px 14px;
  border-radius: 9px;
  cursor: pointer;
  transition: background 0.15s, color 0.15s;
}

.nav-btn:hover {
  background: var(--surface-muted);
  color: var(--text);
}

.nav-btn.active {
  background: #eef2ff;
  color: var(--primary);
}

/* Основная область */
.main-content {
  padding-top: 24px;
  padding-bottom: 48px;
}

.section-heading {
  font-size: 20px;
  font-weight: 700;
  margin: 0 0 14px;
}

/* Панели на главной */
.home-top-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  margin-bottom: 26px;
}

.panel {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px 20px;
  box-shadow: var(--shadow);
}

.panel-title {
  font-size: 15px;
  font-weight: 700;
  margin-bottom: 6px;
}

.panel-desc,
.panel-hint {
  font-size: 13px;
  color: var(--text-muted);
  margin: 0 0 12px;
}

.panel-hint {
  margin: 10px 0 0;
  color: var(--text-soft);
}

.overall-text {
  font-size: 15px;
  font-weight: 600;
  margin: 4px 0 10px;
}

.stepper-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
}

.stepper-label {
  font-size: 14px;
  font-weight: 600;
}

.stepper {
  display: inline-flex;
  align-items: center;
  border: 1px solid var(--border);
  border-radius: 10px;
  overflow: hidden;
  background: var(--surface-muted);
}

.stepper-btn {
  width: 36px;
  height: 36px;
  border: none;
  background: transparent;
  font-size: 18px;
  font-weight: 600;
  color: var(--text);
  cursor: pointer;
}

.stepper-btn:hover:not(:disabled) {
  background: #e2e8f0;
}

.stepper-btn:disabled {
  opacity: 0.4;
  cursor: default;
}

.stepper-input {
  width: 48px;
  height: 36px;
  border: none;
  border-left: 1px solid var(--border);
  border-right: 1px solid var(--border);
  text-align: center;
  font-size: 15px;
  font-weight: 700;
  background: var(--surface);
  color: var(--text);
}

.stepper-input::-webkit-inner-spin-button,
.stepper-input::-webkit-outer-spin-button {
  -webkit-appearance: none;
  margin: 0;
}

/* Прогресс-бары */
.progress-track {
  width: 100%;
  height: 8px;
  background: #e2e8f0;
  border-radius: 999px;
  overflow: hidden;
}

.progress-track-lg {
  height: 10px;
}

.progress-fill {
  height: 100%;
  background: var(--topic-accent, var(--primary));
  border-radius: 999px;
  transition: width 0.25s ease;
}

/* Карточки тем */
.topics-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 16px;
}

.topic-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-top: 4px solid var(--topic-accent, var(--primary));
  border-radius: var(--radius);
  padding: 18px;
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.topic-card.is-completed {
  border-color: var(--success-border);
  border-top-color: var(--success);
  background: linear-gradient(180deg, #f4fbf8 0%, #ffffff 45%);
}

.topic-card.is-completed .progress-fill {
  background: var(--success);
}

.topic-card-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 8px;
}

.topic-title {
  font-size: 17px;
  font-weight: 700;
  margin: 0;
  line-height: 1.3;
}

.topic-desc {
  font-size: 13px;
  color: var(--text-muted);
  margin: 0;
  flex: 1;
}

.topic-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 4px;
}

/* Бейджи */
.badge {
  display: inline-flex;
  align-items: center;
  padding: 3px 9px;
  border-radius: 999px;
  font-size: 12px;
  font-weight: 600;
  white-space: nowrap;
}

.badge-neutral {
  background: #f1f5f9;
  color: var(--text-muted);
}

.badge-success {
  background: var(--success-bg);
  color: var(--success);
}

.badge-warn {
  background: var(--warn-bg);
  color: var(--warn);
}

/* Кнопки */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  border: 1px solid transparent;
  border-radius: 10px;
  padding: 9px 15px;
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s, border-color 0.15s, transform 0.05s;
}

.btn:active {
  transform: translateY(1px);
}

.btn-sm {
  padding: 6px 11px;
  font-size: 13px;
}

.btn-lg {
  padding: 13px 22px;
  font-size: 16px;
}

.btn-primary {
  background: var(--primary);
  color: #fff;
}

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

.btn-secondary {
  background: #f1f5f9;
  color: var(--text);
  border-color: var(--border);
}

.btn-secondary:hover {
  background: #e2e8f0;
}

.btn-ghost {
  background: transparent;
  color: var(--text-muted);
}

.btn-ghost:hover {
  background: #f1f5f9;
  color: var(--text);
}

.btn-danger-text {
  color: var(--danger);
}

.btn-danger-text:hover {
  background: var(--danger-bg);
  color: var(--danger);
}

.btn-correct {
  background: var(--success);
  color: #fff;
  flex: 1;
}

.btn-correct:hover {
  background: #047857;
}

.btn-wrong {
  background: var(--danger);
  color: #fff;
  flex: 1;
}

.btn-wrong:hover {
  background: var(--danger-hover);
}

.kbd-hint {
  font-size: 11px;
  font-weight: 600;
  padding: 2px 6px;
  border-radius: 5px;
  background: rgba(255, 255, 255, 0.22);
}

/* Экран тренировки */
.study-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 10px;
}

.study-meta {
  text-align: right;
}

.study-topic-title {
  font-size: 15px;
  font-weight: 700;
}

.study-counter {
  font-size: 13px;
  color: var(--text-soft);
}

.study-progress-track {
  margin-bottom: 20px;
}

.flashcard {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 18px;
  padding: 26px;
  box-shadow: var(--shadow);
  max-width: 740px;
  margin: 0 auto;
}

.flashcard-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 14px;
}

.card-number {
  font-size: 13px;
  font-weight: 600;
  color: var(--text-soft);
  background: var(--surface-muted);
  padding: 4px 10px;
  border-radius: 8px;
}

.streak-wrap {
  display: flex;
  align-items: center;
  gap: 8px;
}

.streak-dots {
  display: flex;
  gap: 5px;
}

.streak-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: #e2e8f0;
}

.streak-dot.filled {
  background: var(--success);
}

.streak-label {
  font-size: 13px;
  font-weight: 600;
  color: var(--text-muted);
}

.card-title {
  font-size: 24px;
  font-weight: 700;
  margin: 0 0 22px;
  line-height: 1.3;
}

.reveal-wrap {
  display: flex;
  justify-content: center;
  padding: 8px 0;
}

.answer-section {
  border-top: 1px solid var(--border);
  padding-top: 20px;
  margin-top: 6px;
}

.formula-box {
  background: var(--surface-muted);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 18px 14px;
  margin-bottom: 18px;
  overflow-x: auto;
  text-align: center;
}

.formula-display {
  font-size: 1.35rem;
}

.explanation-block {
  margin-bottom: 22px;
}

.block-label {
  font-size: 12px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--text-soft);
  margin: 14px 0 6px;
}

.block-text {
  margin: 0;
  font-size: 15px;
  color: var(--text);
}

.variables-list {
  margin: 0;
  padding-left: 18px;
  display: flex;
  flex-direction: column;
  gap: 6px;
  font-size: 14px;
}

.var-symbol {
  font-weight: 600;
}

.answer-actions {
  display: flex;
  gap: 12px;
}

/* Экран завершения темы */
.done-panel {
  max-width: 540px;
  margin: 20px auto;
  text-align: center;
  padding: 34px 24px;
}

.done-icon {
  width: 56px;
  height: 56px;
  border-radius: 50%;
  background: var(--success-bg);
  color: var(--success);
  font-size: 28px;
  font-weight: 700;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 14px;
}

.done-title {
  margin: 0 0 8px;
  font-size: 22px;
}

.done-desc {
  margin: 0 0 22px;
  color: var(--text-muted);
}

.done-actions {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 10px;
}

/* Статистика */
.stats-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 12px;
  margin-bottom: 14px;
}

.stats-header .section-heading {
  margin: 0;
}

.stats-tools {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.file-label {
  cursor: pointer;
}

.stats-filters {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 12px;
  margin-bottom: 16px;
}

.tabs {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.tab-btn {
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text-muted);
  font-size: 13px;
  font-weight: 600;
  padding: 7px 12px;
  border-radius: 9px;
  cursor: pointer;
}

.tab-btn.active {
  background: var(--primary);
  border-color: var(--primary);
  color: #fff;
}

.filter-right {
  display: flex;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
}

.checkbox-label {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 13px;
  color: var(--text-muted);
  cursor: pointer;
}

.select-input {
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  font-size: 13px;
  font-weight: 600;
  padding: 7px 10px;
  border-radius: 9px;
}

.stats-summary {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
  margin-bottom: 16px;
}

.stat-box {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 14px 16px;
  display: flex;
  flex-direction: column;
  gap: 2px;
}

.stat-box-success {
  border-color: var(--success-border);
  background: var(--success-bg);
}

.stat-box-warn {
  border-color: #fde68a;
  background: var(--warn-bg);
}

.stat-value {
  font-size: 22px;
  font-weight: 700;
}

.stat-label {
  font-size: 12px;
  color: var(--text-muted);
}

.stats-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.stats-row {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 14px 16px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.stats-row.is-learned {
  border-left: 4px solid var(--success);
}

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

.stats-row-meta {
  font-size: 12px;
  color: var(--text-soft);
  margin-bottom: 2px;
}

.stats-row-title {
  font-size: 15px;
  font-weight: 700;
}

.stats-row-formula {
  margin-top: 6px;
  font-size: 15px;
  color: var(--text-muted);
  overflow-x: auto;
}

.stats-row-metrics {
  display: flex;
  align-items: center;
  gap: 14px;
  flex-shrink: 0;
}

.stats-streak {
  font-size: 13px;
  font-weight: 600;
  color: var(--text-muted);
  min-width: 92px;
  text-align: right;
}

.stats-counts {
  display: flex;
  gap: 8px;
  font-size: 13px;
  font-weight: 600;
  min-width: 78px;
  justify-content: flex-end;
}

.count-ok {
  color: var(--success);
}

.count-err {
  color: var(--danger);
}

.empty-state {
  background: var(--surface);
  border: 1px dashed var(--border);
  border-radius: 12px;
  padding: 32px;
  text-align: center;
  color: var(--text-soft);
}

/* Адаптивность */
@media (max-width: 860px) {
  .topics-grid {
    grid-template-columns: 1fr;
  }

  .home-top-grid {
    grid-template-columns: 1fr;
  }

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

@media (max-width: 640px) {
  .flashcard {
    padding: 18px;
  }

  .card-title {
    font-size: 20px;
  }

  .answer-actions {
    flex-direction: column-reverse;
  }

  .kbd-hint {
    display: none;
  }

  .stats-row {
    flex-direction: column;
    align-items: flex-start;
  }

  .stats-row-metrics {
    width: 100%;
    justify-content: space-between;
  }
}