:root {
  --background: #f7fafc;
  --surface: #ffffff;
  --text: #1a2838;
  --text-muted: #5a6b7d;
  --primary: #2b6cb0;
  --primary-hover: #245a94;
  --secondary: #319795;
  --success: #2f855a;
  --danger: #c0564b;
  --border: #d9e2ec;

  --primary-soft: #e8f2fb;
  --secondary-soft: #e6f5f4;
  --success-soft: #e8f5ed;
  --danger-soft: #faeceb;
  --danger-hover: #a3463d;
  --background-admin: #f2f6fa;
  --admin-bar: #1e3148;
  --admin-bar-text: #eef3f8;
  --warning-surface: #edf4f8;
  --on-primary: #ffffff;
  --btn-muted: #eef2f6;
  --shadow: 0 10px 28px rgba(26, 40, 56, 0.08);
  --radius: 1.15rem;
  --font: system-ui, -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

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

html {
  font-size: 100%;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: var(--font);
  color: var(--text);
  background: var(--background);
  line-height: 1.5;
}

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

a:focus-visible,
button:focus-visible,
input:focus-visible,
select:focus-visible,
textarea:focus-visible {
  outline: 3px solid var(--primary);
  outline-offset: 2px;
}

.skip-link {
  position: absolute;
  left: 0.75rem;
  top: -3rem;
  background: var(--primary);
  color: var(--on-primary);
  padding: 0.5rem 0.8rem;
  border-radius: 0.5rem;
  z-index: 10;
}

.skip-link:focus {
  top: 0.75rem;
}

.page {
  width: min(44rem, calc(100% - 1.5rem));
  margin: 0 auto;
  padding: 1.25rem 0 3rem;
}

.page-learn {
  width: min(40rem, calc(100% - 1.25rem));
}

.page-overview {
  width: min(52rem, calc(100% - 1.25rem));
}

.hero-compact {
  margin-bottom: 1.25rem;
}

.learn-tree {
  display: grid;
  gap: 1.5rem;
}

.learn-tree-class {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  overflow: hidden;
}

.learn-tree-class-title {
  margin: 0;
  padding: 1rem 1.15rem;
  font-size: clamp(1.35rem, 4vw, 1.65rem);
  font-weight: 700;
  background: var(--primary-soft);
  color: var(--text);
}

.learn-tree-class-body {
  padding: 1rem 1.15rem 1.15rem;
}

.learn-tree-subject {
  padding: 0 0 1rem;
}

.learn-tree-subject:not(:last-child) {
  margin-bottom: 0.25rem;
}

.learn-tree-subject-title {
  margin: 0 0 0.65rem;
  padding-left: 0.15rem;
  font-size: 1.12rem;
  font-weight: 650;
  color: var(--text);
}

.learn-tree-sets {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 0.65rem;
}

.learn-tree-set {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 0.65rem 1rem;
  padding: 0.75rem 0.85rem;
  background: var(--background);
  border: 1px solid var(--border);
  border-radius: 0.85rem;
  margin-left: 1.25rem;
}

.learn-tree-set-main {
  flex: 1 1 12rem;
  min-width: 0;
}

.learn-tree-set-title {
  display: block;
  font-weight: 650;
  line-height: 1.35;
}

.learn-tree-set-meta {
  display: block;
  margin-top: 0.15rem;
  font-size: 0.92rem;
  color: var(--text-muted);
}

.learn-tree-set-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  flex: 0 1 auto;
}

.intro-block {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 1.1rem 1.2rem;
  margin-bottom: 1rem;
}

.intro-block h2 {
  margin: 0 0 0.75rem;
  font-size: 1.15rem;
}

.intro-text {
  margin: 0;
  white-space: pre-wrap;
  line-height: 1.55;
}

.term-list {
  margin: 0;
  display: grid;
  gap: 0.85rem;
}

.term-item dt {
  font-weight: 700;
  margin: 0 0 0.2rem;
}

.term-item dd {
  margin: 0;
  color: var(--text);
}

.intro-actions {
  margin-top: 1.25rem;
}

.intro-mode-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.65rem;
}

.btn-tree {
  min-height: 2.75rem;
  min-width: 7.5rem;
  padding-left: 1rem;
  padding-right: 1rem;
  font-size: 0.95rem;
  background: var(--surface);
  color: var(--text);
  border: 1px solid var(--border);
  box-shadow: inset 0 0 0 0 transparent;
}

.btn-tree:hover {
  background: var(--secondary-soft);
  border-color: color-mix(in srgb, var(--primary) 35%, var(--border));
  color: var(--text);
}

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

@media (max-width: 480px) {
  .learn-tree-set {
    flex-direction: column;
    align-items: stretch;
    margin-left: 0.75rem;
  }

  .learn-tree-set-actions {
    flex-direction: column;
  }

  .btn-tree {
    width: 100%;
    min-width: 0;
  }
}

.hero {
  margin: 1.5rem 0 1.75rem;
}

.hero h1,
.admin-main h1 {
  margin: 0 0 0.35rem;
  font-size: clamp(1.8rem, 6vw, 2.4rem);
  letter-spacing: -0.03em;
  font-weight: 700;
}

.lede {
  margin: 0;
  color: var(--text-muted);
  font-size: 1.1rem;
}

.crumb {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  align-items: center;
  color: var(--text-muted);
  font-size: 0.95rem;
}

.crumb a {
  text-decoration: none;
  color: var(--secondary);
}

.choice-grid {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.9rem;
}

.choice-grid-wide {
  grid-template-columns: 1fr;
}

.choice-card {
  display: flex;
  flex-direction: column;
  justify-content: center;
  min-height: 5.5rem;
  padding: 1.1rem 1.15rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  text-decoration: none;
  color: inherit;
}

.choice-card:hover {
  border-color: var(--primary);
}

.choice-card-title {
  font-size: 1.35rem;
  font-weight: 700;
}

.choice-card-meta {
  color: var(--text-muted);
  font-size: 0.95rem;
}

.empty,
.card-count {
  color: var(--text-muted);
}

.progress {
  margin: 0.75rem 0 1rem;
  font-size: 1.05rem;
  font-weight: 600;
}

.flashcard {
  min-height: 14rem;
  padding: 1.4rem 1.25rem;
  background: var(--surface);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  border: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  justify-content: center;
}

.flashcard-quiz {
  position: relative;
  overflow: hidden;
  isolation: isolate;
}

.quiz-sash {
  position: absolute;
  z-index: 2;
  left: 50%;
  top: 50%;
  width: 145%;
  max-width: none;
  padding: 0.55rem 1rem;
  margin: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  transform: translate(-50%, -50%) rotate(-28deg);
  pointer-events: none;
  box-shadow: 0 4px 16px rgba(26, 40, 56, 0.12);
}

.quiz-sash-idle {
  display: none;
}

.quiz-sash-correct {
  background: color-mix(in srgb, var(--success) 88%, #ffffff);
  color: #ffffff;
}

.quiz-sash-wrong {
  background: color-mix(in srgb, var(--danger) 88%, #ffffff);
  color: #ffffff;
}

.quiz-sash-text {
  display: block;
  width: 100%;
  max-width: 36rem;
  font-size: clamp(0.95rem, 3.8vw, 1.25rem);
  font-weight: 800;
  letter-spacing: 0.02em;
  line-height: 1.25;
  text-wrap: balance;
}

.quiz-hint {
  margin: 0.75rem 0 0;
  font-size: 0.95rem;
  color: var(--text-muted);
}

.cloze-text {
  margin: 0;
  font-size: clamp(1.1rem, 4vw, 1.4rem);
  line-height: 1.5;
  font-weight: 650;
  white-space: pre-wrap;
}

.cloze-label {
  display: block;
  margin: 1.1rem 0 0.4rem;
  font-size: 0.95rem;
  color: var(--text-muted);
}

.cloze-input {
  width: 100%;
  font: inherit;
  font-size: 1.1rem;
  padding: 0.75rem 0.85rem;
  border: 2px solid var(--border);
  border-radius: 0.85rem;
  background: var(--surface);
  color: var(--text);
}

.cloze-input:focus {
  outline: 3px solid var(--primary);
  outline-offset: 2px;
  border-color: var(--primary);
}

.cloze-hint {
  margin: 0.75rem 0 0;
  padding: 0.65rem 0.8rem;
  border-radius: 0.75rem;
  background: var(--primary-soft);
  border: 1px solid var(--border);
  font-weight: 650;
  letter-spacing: 0.04em;
  color: var(--text);
  word-break: break-word;
}

.cloze-actions {
  grid-template-columns: 1fr 1fr;
}

.cloze-actions #next-card:not([hidden]) {
  grid-column: 1 / -1;
}

@media (max-width: 480px) {
  .quiz-sash {
    width: 160%;
    padding: 0.5rem 0.75rem;
    transform: translate(-50%, -50%) rotate(-32deg);
  }

  .quiz-sash-text {
    font-size: clamp(0.85rem, 3.6vw, 1.05rem);
  }
}

.question {
  margin: 0;
  font-size: clamp(1.2rem, 4.4vw, 1.55rem);
  line-height: 1.35;
  font-weight: 650;
}

.answer,
.status-text {
  margin: 1rem 0 0;
  font-size: 1.1rem;
}

.status-hint {
  color: var(--text-muted);
  font-size: 0.98rem;
}

.status-ok {
  color: var(--success);
  font-weight: 700;
}

.status-bad {
  color: var(--danger);
  font-weight: 700;
}

.learn-actions {
  display: grid;
  grid-template-columns: 1fr;
  gap: 0.75rem;
  margin-top: 1rem;
}

[hidden] {
  display: none !important;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 3rem;
  padding: 0.7rem 1.1rem;
  border: 0;
  border-radius: 0.9rem;
  font: inherit;
  font-weight: 650;
  text-decoration: none;
  cursor: pointer;
  color: var(--text);
  background: var(--btn-muted);
}

.btn-block {
  width: 100%;
}

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

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

.btn-secondary {
  background: var(--surface);
  color: var(--text);
  box-shadow: inset 0 0 0 2px var(--border);
}

.btn-danger {
  background: var(--danger);
  color: var(--on-primary);
}

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

.btn-small {
  min-height: 2.3rem;
  padding: 0.3rem 0.7rem;
  border-radius: 0.6rem;
  font-size: 0.9rem;
}

.choice-btn:disabled {
  opacity: 1;
  cursor: default;
}

.choice-options {
  display: grid;
  gap: 0.75rem;
  margin-top: 1rem;
}

.choice-btn {
  min-height: 3.2rem;
  padding: 0.85rem 1rem;
  text-align: left;
  background: var(--surface);
  border: 2px solid var(--border);
  border-radius: 0.95rem;
  font: inherit;
  cursor: pointer;
}

.choice-btn[aria-pressed="true"],
.choice-btn.is-selected {
  border-color: var(--primary);
  background: var(--primary-soft);
}

.choice-btn.is-correct {
  border-color: var(--success);
  background: var(--success-soft);
  color: var(--text);
}

.choice-btn.is-wrong {
  border-color: var(--danger);
  background: var(--danger-soft);
  color: var(--text);
}

.choice-btn .choice-state {
  display: block;
  font-size: 0.85rem;
  font-weight: 700;
  margin-top: 0.2rem;
}

.summary {
  background: var(--surface);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 1.4rem 1.2rem;
  border: 1px solid var(--border);
}

.summary-stats {
  list-style: none;
  margin: 1rem 0 1.4rem;
  padding: 0;
  display: grid;
  gap: 0.6rem;
}

.summary-stats li {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  padding: 0.7rem 0;
  border-bottom: 1px solid var(--border);
}

.flash-list {
  display: grid;
  gap: 0.5rem;
  margin-bottom: 1rem;
}

.flash {
  margin: 0;
  padding: 0.75rem 0.9rem;
  border-radius: 0.75rem;
}

.flash-success {
  background: var(--success-soft);
}

.flash-error,
.flash-danger {
  background: var(--danger-soft);
}

.flash-warning,
.flash-message {
  background: var(--warning-surface);
}

.layout-admin {
  background: var(--background-admin);
}

.admin-top {
  background: var(--admin-bar);
  color: var(--admin-bar-text);
}

.admin-top a {
  color: inherit;
  text-decoration: none;
}

.admin-top-inner {
  width: min(70rem, calc(100% - 1.5rem));
  margin: 0 auto;
  padding: 0.85rem 0;
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem 1.2rem;
  align-items: center;
  justify-content: space-between;
}

.admin-brand {
  font-weight: 750;
}

.admin-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem 1rem;
  font-size: 0.95rem;
}

.admin-main {
  width: min(70rem, calc(100% - 1.5rem));
  margin: 0 auto;
  padding: 1.4rem 0 3rem;
}

.admin-main h1 {
  font-size: 1.7rem;
}

.admin-main h2 {
  font-size: 1.15rem;
  margin: 1.5rem 0 0.75rem;
}

.stat-grid,
.action-list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.stat-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.75rem;
}

.stat-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 0.9rem;
  padding: 0.9rem 1rem;
}

.stat-card span {
  display: block;
  color: var(--text-muted);
}

.stat-card strong {
  font-size: 1.6rem;
}

.action-list {
  display: grid;
  gap: 0.6rem;
}

.page-head,
.actions,
.inline-form {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  align-items: center;
}

.page-head {
  justify-content: space-between;
  margin: 0.5rem 0 1rem;
}

.stack-form {
  display: grid;
  gap: 0.55rem;
  max-width: 36rem;
}

.stack-form input[type="text"],
.stack-form input[type="password"],
.stack-form input[type="number"],
.stack-form input[type="file"],
.stack-form select,
.stack-form textarea,
.inline-form input[type="text"] {
  font: inherit;
  padding: 0.55rem 0.7rem;
  border: 1px solid var(--border);
  border-radius: 0.6rem;
  background: var(--surface);
  width: 100%;
}

.inline-form input[type="text"] {
  width: auto;
  min-width: 8rem;
}

.field-hint {
  margin: -0.35rem 0 0;
  font-size: 0.92rem;
  color: var(--text-muted);
}

.sets-search {
  display: grid;
  gap: 0.45rem;
  margin: 0.85rem 0 1rem;
}

.sets-search-field {
  position: relative;
  display: flex;
  align-items: center;
}

.sets-search-icon {
  position: absolute;
  left: 0.75rem;
  pointer-events: none;
  font-size: 0.95rem;
  line-height: 1;
}

.sets-search-input {
  width: 100%;
  font: inherit;
  font-size: 1rem;
  padding: 0.7rem 2.4rem 0.7rem 2.35rem;
  border: 2px solid var(--border);
  border-radius: 0.85rem;
  background: var(--surface);
  color: var(--text);
}

.sets-search-input:focus {
  outline: 3px solid var(--primary);
  outline-offset: 2px;
  border-color: var(--primary);
}

.sets-search-input::-webkit-search-cancel-button {
  -webkit-appearance: none;
  appearance: none;
}

.sets-search-clear {
  position: absolute;
  right: 0.45rem;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 1.85rem;
  height: 1.85rem;
  border: 0;
  border-radius: 999px;
  background: transparent;
  color: var(--text-muted);
  font-size: 1.25rem;
  line-height: 1;
  cursor: pointer;
}

.sets-search-clear:hover,
.sets-search-clear:focus-visible {
  background: var(--primary-soft);
  color: var(--text);
  outline: none;
}

.sets-search-count {
  margin: 0;
  font-size: 0.9rem;
  color: var(--text-muted);
}

.sets-search-empty {
  margin-top: 0.5rem;
}

.sets-search-empty .field-hint {
  margin-top: 0.25rem;
}

.module-toggles {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  align-items: center;
}

.module-chip {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  margin: 0;
  padding: 0.28rem 0.55rem;
  border: 1px solid var(--border);
  border-radius: 0.55rem;
  background: var(--surface);
  font-size: 0.86rem;
  font-weight: 600;
  color: var(--text-muted);
  cursor: pointer;
  user-select: none;
}

.module-chip.is-on {
  border-color: var(--primary);
  background: var(--primary-soft);
  color: var(--text);
}

.module-chip input {
  width: 0.95rem;
  height: 0.95rem;
  margin: 0;
  accent-color: var(--primary);
}

.module-toggles.is-saving .module-chip {
  opacity: 0.65;
  pointer-events: none;
}

.module-saving {
  font-size: 0.8rem;
  color: var(--text-muted);
}

.check-label {
  display: flex;
  gap: 0.5rem;
  align-items: center;
}

fieldset {
  border: 1px solid var(--border);
  border-radius: 0.8rem;
  padding: 0.9rem;
  display: grid;
  gap: 0.45rem;
}

.table-wrap {
  overflow-x: auto;
}

.data-table {
  width: 100%;
  border-collapse: collapse;
  background: var(--surface);
  border-radius: 0.8rem;
}

.data-table th,
.data-table td {
  text-align: left;
  padding: 0.7rem;
  border-bottom: 1px solid var(--border);
  vertical-align: top;
}

.card-admin-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 0.8rem;
}

.card-admin {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 0.9rem;
  padding: 0.9rem 1rem;
}

.card-admin-question {
  margin: 0 0 0.6rem;
  font-weight: 650;
}

.answer-list {
  margin: 0;
  padding: 0;
  list-style: none;
  display: grid;
  gap: 0.35rem;
}

.answer-list li {
  display: flex;
  gap: 0.5rem;
  align-items: baseline;
}

.answer-index {
  display: inline-flex;
  min-width: 1.4rem;
  justify-content: center;
  font-weight: 700;
  color: var(--text-muted);
}

.is-correct {
  background: var(--success-soft);
  border-radius: 0.45rem;
  padding: 0.15rem 0.4rem;
}

.tag {
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--success);
}

.meta {
  color: var(--text-muted);
  font-size: 0.95rem;
}

.warning-text,
.field-error {
  color: var(--danger);
}

.warning-box {
  background: var(--warning-surface);
  border-radius: 0.8rem;
  padding: 0.9rem 1rem;
}

.login-card {
  max-width: 24rem;
  margin: 2rem auto;
  background: var(--surface);
  padding: 1.4rem 1.2rem;
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  border: 0;
}

@media (min-width: 720px) {
  .choice-grid {
    grid-template-columns: repeat(auto-fill, minmax(9.5rem, 1fr));
  }

  .choice-grid-wide {
    grid-template-columns: 1fr 1fr;
  }

  .learn-actions:has(#again:not([hidden])) {
    grid-template-columns: 1fr 1fr;
  }

  .choice-options {
    grid-template-columns: 1fr 1fr;
  }

  .stat-grid {
    grid-template-columns: repeat(4, 1fr);
  }

  .action-list {
    grid-template-columns: repeat(2, max-content);
  }
}