:root {
  --bg: #f6f8fb;
  --surface: #ffffff;
  --surface-2: #eef4f8;
  --ink: #101828;
  --muted: #637083;
  --line: #d9e2ea;
  --teal: #007f86;
  --teal-dark: #005d67;
  --blue: #2563eb;
  --green: #047857;
  --red: #dc2626;
  --amber: #d97706;
  --shadow: 0 18px 55px rgba(16, 24, 40, 0.08);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
}

button,
input,
select,
textarea {
  font: inherit;
}

button {
  cursor: pointer;
}

button:disabled {
  cursor: not-allowed;
  opacity: 0.45;
}

a {
  color: var(--teal-dark);
}

svg {
  width: 20px;
  height: 20px;
  fill: currentColor;
}

.app-shell {
  min-height: 100vh;
  display: grid;
  grid-template-columns: 280px 1fr;
  background: var(--bg);
  color: var(--ink);
}

.app-shell[data-theme="dark"] {
  --bg: #0e1724;
  --surface: #111d2d;
  --surface-2: #17263a;
  --ink: #e8eef8;
  --muted: #9aabc2;
  --line: #2a3b52;
  --shadow: 0 18px 55px rgba(0, 0, 0, 0.25);
}

.sidebar {
  background: linear-gradient(180deg, #042f3d 0%, #071c2c 100%);
  color: white;
  padding: 26px 16px;
  display: flex;
  flex-direction: column;
  gap: 22px;
  min-height: 100vh;
}

.brand {
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 0 8px 14px;
}

.brand strong {
  display: block;
  font-size: 24px;
  line-height: 1;
}

.brand span {
  color: #32d3c7;
  font-weight: 700;
}

.brand-mark {
  width: 54px;
  height: 54px;
  display: grid;
  place-items: center;
  border-radius: 12px;
  background: linear-gradient(135deg, #0694a2, #0f766e);
  font-size: 11px;
  font-weight: 900;
  letter-spacing: 0.08em;
}

.switch-panel {
  display: grid;
  gap: 10px;
  padding: 12px;
  border: 1px solid rgba(255, 255, 255, 0.16);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.07);
}

.switch-panel label {
  display: grid;
  gap: 6px;
}

.switch-panel span {
  color: rgba(255, 255, 255, 0.72);
  font-size: 12px;
  font-weight: 800;
  text-transform: uppercase;
}

.switch-panel select {
  width: 100%;
  min-height: 40px;
  background: rgba(255, 255, 255, 0.95);
  color: #0f172a;
  border-color: rgba(255, 255, 255, 0.28);
}

nav {
  display: grid;
  gap: 8px;
}

.nav-button {
  border: 0;
  color: rgba(255, 255, 255, 0.82);
  background: transparent;
  display: flex;
  gap: 12px;
  align-items: center;
  text-align: left;
  padding: 14px 13px;
  border-radius: 8px;
}

.nav-button:hover,
.nav-button.active {
  background: linear-gradient(135deg, rgba(0, 127, 134, 0.95), rgba(0, 99, 112, 0.86));
  color: white;
}

.nav-button strong,
.nav-button small {
  display: block;
}

.nav-button small {
  color: rgba(255, 255, 255, 0.72);
  margin-top: 3px;
}

.session-card {
  margin-top: auto;
  border-top: 1px solid rgba(255, 255, 255, 0.16);
  padding: 20px 8px;
}

.session-card span,
.session-card small {
  color: rgba(255, 255, 255, 0.7);
}

.session-card strong {
  display: block;
  font-size: 28px;
  margin: 6px 0 10px;
}

.progress {
  height: 8px;
  border-radius: 999px;
  background: var(--surface-2);
  overflow: hidden;
}

.progress i {
  display: block;
  height: 100%;
  background: var(--teal);
}

.workspace {
  min-width: 0;
  padding: 24px;
}

.topbar {
  display: flex;
  justify-content: space-between;
  gap: 24px;
  align-items: center;
  margin-bottom: 22px;
}

.topbar p {
  margin: 0 0 6px;
  color: var(--muted);
  font-size: 14px;
}

h1,
h2,
h3,
h4,
p {
  margin-top: 0;
}

h1,
h2,
h3,
h4 {
  color: var(--ink);
}

h1 {
  margin-bottom: 0;
  font-size: 30px;
}

.search {
  min-width: min(420px, 42vw);
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 8px;
  display: grid;
  grid-template-columns: auto 1fr;
  align-items: center;
  gap: 10px;
  padding: 0 14px;
  box-shadow: 0 1px 0 rgba(16, 24, 40, 0.03);
}

.search span {
  color: var(--muted);
  font-size: 12px;
  font-weight: 700;
  text-transform: uppercase;
}

.search input {
  width: 100%;
  border: 0;
  background: transparent;
  color: var(--ink);
  padding: 14px 0;
  outline: 0;
}

.study-grid,
.exam-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 320px;
  gap: 18px;
}

.study-grid {
  grid-template-areas:
    "filters filters"
    "center right";
}

.exam-grid {
  grid-template-areas: "center right";
}

.filters {
  grid-area: filters;
  display: grid;
  grid-template-columns: repeat(3, minmax(180px, 1fr)) auto;
  gap: 12px;
  align-items: end;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 14px;
}

.filters label,
.notes-panel {
  display: grid;
  gap: 6px;
}

.filters span,
.notes-panel span {
  color: var(--muted);
  font-size: 12px;
  font-weight: 800;
  text-transform: uppercase;
}

select,
textarea {
  width: 100%;
  background: var(--surface);
  color: var(--ink);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 10px 12px;
}

.filter-count {
  color: var(--muted);
  font-weight: 800;
  padding: 10px 0;
}

.center-column {
  min-width: 0;
}

.study-grid > .center-column,
.exam-grid > .center-column {
  grid-area: center;
}

.right-rail {
  display: grid;
  gap: 14px;
  align-content: start;
}

.study-grid > .right-rail,
.exam-grid > .right-rail {
  grid-area: right;
}

.question-nav,
.exam-status {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 12px;
  color: var(--muted);
}

.question-panel,
.rail-card,
.result-card,
.list-card,
.weak-summary,
.source-intro,
.source-note,
.book-grid article,
.exam-start {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: var(--shadow);
}

.question-panel {
  padding: 20px;
}

.question-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  align-items: center;
  color: var(--muted);
  margin-bottom: 18px;
}

.question-meta span {
  background: var(--surface-2);
  border-radius: 7px;
  padding: 7px 10px;
  font-size: 13px;
  font-weight: 800;
}

.question-meta .difficulty {
  color: white;
  background: var(--teal);
  text-transform: uppercase;
}

.difficulty.hard {
  background: var(--amber);
}

.difficulty.easy {
  background: var(--green);
}

.question-panel h2 {
  color: var(--ink);
  font-size: clamp(21px, 2vw, 29px);
  line-height: 1.26;
  margin-bottom: 18px;
  letter-spacing: 0;
}

.choice-stack {
  display: grid;
  gap: 10px;
}

.choice {
  display: grid;
  grid-template-columns: 38px 1fr;
  gap: 12px;
  align-items: center;
  text-align: left;
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 8px;
  color: var(--ink);
  background: var(--surface);
  padding: 12px;
}

.choice:hover,
.choice.selected {
  border-color: var(--teal);
  background: rgba(0, 127, 134, 0.06);
}

.choice.correct {
  border-color: rgba(4, 120, 87, 0.45);
  background: rgba(4, 120, 87, 0.08);
}

.choice.incorrect {
  border-color: rgba(220, 38, 38, 0.5);
  background: rgba(220, 38, 38, 0.08);
}

.choice-letter {
  width: 34px;
  height: 34px;
  display: grid;
  place-items: center;
  border: 1px solid var(--line);
  border-radius: 50%;
  font-weight: 900;
}

.confidence {
  margin: 16px 0;
  display: grid;
  grid-template-columns: 1fr repeat(5, 62px);
  gap: 10px;
  align-items: stretch;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 10px;
}

.confidence span {
  display: block;
  color: var(--muted);
  font-size: 13px;
  margin-top: 3px;
}

.confidence button {
  border: 1px solid var(--line);
  background: var(--surface);
  color: var(--ink);
  border-radius: 8px;
  font-weight: 900;
}

.confidence button.active {
  border-color: var(--teal);
  color: var(--teal-dark);
  background: rgba(0, 127, 134, 0.08);
}

.muted-panel {
  margin-top: 16px;
  padding: 14px;
  border-radius: 8px;
  background: var(--surface-2);
  color: var(--muted);
}

.explanation {
  margin-top: 16px;
  display: grid;
  grid-template-columns: minmax(0, 1.8fr) minmax(220px, 0.9fr);
  gap: 18px;
  border: 1px solid rgba(4, 120, 87, 0.25);
  background: rgba(4, 120, 87, 0.06);
  border-radius: 8px;
  padding: 18px;
}

.explanation.is-incorrect {
  border-color: rgba(220, 38, 38, 0.26);
  background: rgba(220, 38, 38, 0.05);
}

.explanation h3 {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 10px;
}

.explanation p {
  line-height: 1.55;
}

.explanation aside {
  border-left: 1px solid var(--line);
  padding-left: 18px;
}

.explanation ul {
  padding-left: 18px;
  color: var(--muted);
}

.notes-panel {
  margin-top: 16px;
}

.notes-panel textarea {
  min-height: 84px;
  resize: vertical;
}

.rail-card {
  padding: 18px;
  color: var(--ink);
}

.rail-card h3 {
  color: var(--ink);
}

.domain-row {
  display: grid;
  gap: 7px;
  margin: 14px 0;
}

.domain-row div:first-child {
  display: flex;
  justify-content: space-between;
  gap: 14px;
  font-size: 14px;
  color: var(--ink);
}

.domain-row strong {
  color: var(--ink);
  white-space: nowrap;
}

.jump-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
}

.jump-grid.exam {
  grid-template-columns: repeat(5, 1fr);
}

.jump-grid button {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  color: var(--ink);
  min-height: 38px;
  font-weight: 800;
}

.jump-grid button.active,
.jump-grid button.answered {
  background: var(--teal);
  color: white;
  border-color: var(--teal);
}

.jump-grid button.answered:not(.active) {
  background: rgba(0, 127, 134, 0.12);
  color: var(--teal-dark);
}

.app-shell[data-theme="dark"] .rail-card {
  background: #142236;
  border-color: #314760;
  color: #f2f7ff;
}

.app-shell[data-theme="dark"] .rail-card h3,
.app-shell[data-theme="dark"] .domain-row div:first-child,
.app-shell[data-theme="dark"] .domain-row span,
.app-shell[data-theme="dark"] .domain-row strong {
  color: #f2f7ff;
}

.app-shell[data-theme="dark"] .domain-row .progress {
  background: #263a52;
}

.app-shell[data-theme="dark"] .jump-grid button {
  background: #17263a;
  border-color: #344d68;
  color: #f2f7ff;
}

.app-shell[data-theme="dark"] .jump-grid button.active,
.app-shell[data-theme="dark"] .jump-grid button.answered {
  background: #006c73;
  border-color: #006c73;
  color: #ffffff;
}

.app-shell[data-theme="dark"] .jump-grid button.answered:not(.active) {
  background: rgba(0, 108, 115, 0.3);
  color: #d9fbff;
}

.primary,
.secondary,
.danger,
.icon-button {
  border-radius: 8px;
  border: 1px solid var(--line);
  padding: 11px 14px;
  font-weight: 900;
}

.primary {
  background: var(--teal);
  color: white;
  border-color: var(--teal);
}

.secondary {
  background: var(--surface);
  color: var(--ink);
}

.danger {
  background: rgba(220, 38, 38, 0.08);
  color: var(--red);
  border-color: rgba(220, 38, 38, 0.35);
}

.full {
  width: 100%;
}

.icon-button {
  margin-left: auto;
  width: 42px;
  height: 42px;
  display: grid;
  place-items: center;
  padding: 0;
  background: var(--surface);
  color: var(--muted);
}

.icon-button.active {
  color: var(--teal);
  border-color: var(--teal);
}

.exam-start {
  display: grid;
  grid-template-columns: 1fr 340px;
  gap: 24px;
  padding: 26px;
}

.exam-start h2,
.weak-summary h2,
.source-intro h2 {
  font-size: 34px;
}

.exam-start p,
.weak-summary p,
.source-intro p {
  color: var(--muted);
  line-height: 1.6;
  max-width: 760px;
}

.exam-status {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 14px;
}

.exam-status strong {
  color: var(--teal-dark);
  font-size: 22px;
}

.results-layout {
  display: grid;
  grid-template-columns: 1fr 340px;
  gap: 18px;
  align-items: start;
}

.result-card,
.weak-summary,
.source-intro,
.source-note {
  padding: 24px;
}

.score-ring {
  width: 140px;
  height: 140px;
  border: 12px solid rgba(0, 127, 134, 0.18);
  border-top-color: var(--teal);
  border-radius: 50%;
  display: grid;
  place-items: center;
  font-size: 34px;
  font-weight: 950;
  margin-bottom: 16px;
}

.review-list {
  margin-top: 18px;
  display: grid;
  gap: 8px;
}

.review-row,
.list-card button {
  width: 100%;
  display: grid;
  grid-template-columns: 70px 1fr auto;
  gap: 12px;
  align-items: center;
  text-align: left;
  border: 1px solid var(--line);
  background: var(--surface);
  color: var(--ink);
  border-radius: 8px;
  padding: 12px 14px;
}

.review-row.correct {
  border-left: 5px solid var(--green);
}

.review-row.incorrect {
  border-left: 5px solid var(--red);
}

.weak-layout {
  display: grid;
  gap: 16px;
}

.metric-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(140px, 1fr));
  gap: 12px;
  margin: 20px 0;
}

.metric-grid div {
  background: var(--surface-2);
  border-radius: 8px;
  padding: 16px;
}

.metric-grid span,
.metric-grid strong {
  display: block;
}

.metric-grid span {
  color: var(--muted);
}

.metric-grid strong {
  font-size: 28px;
  margin-top: 6px;
}

.list-card {
  padding: 18px;
  display: grid;
  gap: 8px;
}

.list-card button {
  grid-template-columns: 230px 1fr;
}

.list-card span {
  color: var(--muted);
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.sources-layout {
  display: grid;
  gap: 16px;
}

.book-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 16px;
}

.book-grid article {
  padding: 22px;
}

.book-grid span {
  color: var(--teal);
  font-size: 12px;
  font-weight: 900;
  text-transform: uppercase;
}

.book-grid p,
.source-note li {
  color: var(--muted);
  line-height: 1.55;
}

@media (max-width: 1100px) {
  .app-shell {
    grid-template-columns: 1fr;
  }

  .sidebar {
    min-height: auto;
    position: sticky;
    top: 0;
    z-index: 5;
  }

  nav,
  .filters,
  .metric-grid,
  .book-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .study-grid,
  .exam-grid,
  .results-layout,
  .exam-start {
    grid-template-columns: 1fr;
    grid-template-areas:
      "filters"
      "center"
      "right";
  }
}

@media (max-width: 720px) {
  body {
    background: var(--surface);
  }

  .sidebar {
    position: static;
    min-height: auto;
    padding: 12px;
    gap: 10px;
  }

  .brand {
    padding: 0;
    gap: 10px;
  }

  .brand-mark {
    width: 42px;
    height: 42px;
    border-radius: 8px;
    font-size: 10px;
  }

  .brand strong {
    font-size: 20px;
  }

  .brand span {
    font-size: 13px;
  }

  .switch-panel {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 8px;
    padding: 10px;
  }

  .switch-panel select {
    min-height: 38px;
    padding: 8px 9px;
    font-size: 14px;
  }

  nav {
    grid-template-columns: repeat(4, minmax(0, 1fr));
    gap: 6px;
  }

  .nav-button {
    min-height: 66px;
    flex-direction: column;
    justify-content: center;
    gap: 6px;
    padding: 8px 4px;
    text-align: center;
  }

  .nav-button svg {
    width: 18px;
    height: 18px;
  }

  .nav-button strong {
    font-size: 12px;
    line-height: 1.15;
    overflow-wrap: anywhere;
  }

  .nav-button small {
    display: none;
  }

  .session-card {
    display: grid;
    grid-template-columns: auto 1fr;
    align-items: center;
    column-gap: 10px;
    row-gap: 5px;
    margin-top: 0;
    padding: 8px 4px 0;
  }

  .session-card strong {
    font-size: 18px;
    margin: 0;
  }

  .session-card .progress {
    grid-column: 1 / -1;
    height: 6px;
  }

  .session-card small {
    display: none;
  }

  .sidebar .full {
    min-height: 40px;
    padding: 9px 12px;
  }

  .workspace {
    padding: 14px 12px 18px;
  }

  .topbar,
  .exam-status {
    align-items: stretch;
    flex-direction: column;
  }

  .topbar {
    gap: 12px;
    margin-bottom: 14px;
  }

  .topbar p {
    display: none;
  }

  h1 {
    font-size: 26px;
  }

  .search {
    min-width: 0;
    width: 100%;
    padding: 0 11px;
  }

  .search input {
    padding: 12px 0;
  }

  .filters {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 10px;
    padding: 12px;
  }

  .filters span {
    font-size: 11px;
  }

  .filters select {
    min-height: 38px;
    padding: 8px 9px;
    font-size: 14px;
  }

  .filters label:first-child,
  .filter-count {
    grid-column: 1 / -1;
  }

  .filter-count {
    display: none;
  }

  .metric-grid,
  .book-grid,
  .explanation {
    grid-template-columns: 1fr;
  }

  .question-nav {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    align-items: stretch;
    gap: 8px;
  }

  .question-nav span {
    grid-column: 1 / -1;
    order: -1;
    text-align: center;
  }

  .question-nav .danger {
    grid-column: 1 / -1;
    order: 2;
  }

  .question-panel,
  .rail-card,
  .result-card,
  .list-card,
  .weak-summary,
  .source-intro,
  .source-note,
  .book-grid article,
  .exam-start {
    box-shadow: none;
  }

  .question-panel {
    padding: 14px;
  }

  .question-meta {
    gap: 8px;
    margin-bottom: 14px;
  }

  .question-meta span {
    padding: 6px 8px;
    font-size: 12px;
  }

  .question-panel h2 {
    font-size: 20px;
    line-height: 1.3;
  }

  .choice {
    grid-template-columns: 34px 1fr;
    gap: 9px;
    padding: 10px;
  }

  .choice-letter {
    width: 30px;
    height: 30px;
  }

  .confidence {
    grid-template-columns: repeat(5, minmax(0, 1fr));
    gap: 8px;
    padding: 10px;
  }

  .confidence > div {
    grid-column: 1 / -1;
  }

  .confidence button {
    min-height: 40px;
  }

  .icon-button {
    width: 38px;
    height: 38px;
  }

  .exam-start,
  .result-card,
  .weak-summary,
  .source-intro,
  .source-note {
    padding: 18px;
  }

  .exam-start h2,
  .weak-summary h2,
  .source-intro h2 {
    font-size: 27px;
  }

  .explanation aside {
    border-left: 0;
    border-top: 1px solid var(--line);
    padding-left: 0;
    padding-top: 14px;
  }

  .review-row,
  .list-card button {
    grid-template-columns: 1fr;
  }
}