:root {
  --ink: #172026;
  --muted: #62707a;
  --line: #dbe2e7;
  --surface: #ffffff;
  --soft: #f5f8fb;
  --teal: #087f7a;
  --green: #2e7d32;
  --coral: #d4514c;
  --gold: #b97812;
  --violet: #6950a1;
  --cyan: #1d7795;
  --shadow: 0 18px 50px rgba(23, 32, 38, 0.12);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  color: var(--ink);
  background:
    linear-gradient(90deg, rgba(8, 127, 122, 0.08) 1px, transparent 1px),
    linear-gradient(180deg, rgba(212, 81, 76, 0.06) 1px, transparent 1px),
    #f7fafc;
  background-size: 34px 34px;
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

button {
  font: inherit;
}

.app-shell {
  display: grid;
  grid-template-columns: minmax(280px, 340px) minmax(0, 1fr);
  min-height: 100vh;
}

.sidebar {
  display: flex;
  flex-direction: column;
  gap: 22px;
  padding: 26px;
  background: #ffffff;
  border-right: 1px solid var(--line);
}

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

.brand-mark {
  display: grid;
  flex: 0 0 54px;
  width: 54px;
  height: 54px;
  place-items: center;
  color: white;
  background: var(--teal);
  border-radius: 8px;
  font-weight: 900;
  letter-spacing: 0;
  box-shadow: inset 0 -8px 0 rgba(0, 0, 0, 0.12);
}

.brand p,
.eyebrow {
  margin: 0 0 4px;
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.brand h1,
.topbar h2,
.lesson-panel h3,
.result-panel h2 {
  margin: 0;
  letter-spacing: 0;
}

.brand h1 {
  font-size: 1.15rem;
  line-height: 1.2;
}

.stats-board,
.session-summary {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 8px;
}

.stats-board div,
.session-summary div {
  min-width: 0;
  padding: 13px 10px;
  background: var(--soft);
  border: 1px solid var(--line);
  border-radius: 8px;
}

.stats-board span,
.session-summary span {
  display: block;
  font-size: 1.25rem;
  font-weight: 900;
}

.stats-board small,
.session-summary small {
  display: block;
  margin-top: 4px;
  color: var(--muted);
  font-size: 0.72rem;
  line-height: 1.25;
}

.topic-list {
  display: grid;
  gap: 9px;
  overflow: auto;
  padding-right: 2px;
}

.topic-button {
  display: grid;
  grid-template-columns: 38px 1fr auto;
  align-items: center;
  gap: 11px;
  width: 100%;
  padding: 10px;
  color: var(--ink);
  text-align: left;
  background: #ffffff;
  border: 1px solid var(--line);
  border-radius: 8px;
  cursor: pointer;
}

.topic-button:hover,
.topic-button:focus-visible,
.topic-button.active {
  border-color: var(--topic-color);
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--topic-color), transparent 82%);
  outline: none;
}

.topic-icon {
  display: grid;
  width: 38px;
  height: 38px;
  place-items: center;
  color: white;
  background: var(--topic-color);
  border-radius: 8px;
  font-weight: 900;
}

.topic-button strong {
  display: block;
  font-size: 0.92rem;
}

.topic-button small {
  display: block;
  margin-top: 3px;
  color: var(--muted);
}

.topic-percent {
  color: var(--topic-color);
  font-weight: 900;
}

.workspace {
  display: flex;
  flex-direction: column;
  gap: 18px;
  min-width: 0;
  padding: 26px;
}

.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
}

.topbar h2 {
  font-size: clamp(1.35rem, 3vw, 2rem);
}

.mode-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  justify-content: flex-end;
}

.mode-button,
.ghost-button,
.primary-button,
.text-button {
  min-height: 42px;
  border-radius: 8px;
  cursor: pointer;
  transition: transform 150ms ease, box-shadow 150ms ease, background 150ms ease;
}

.mode-button {
  padding: 0 14px;
  color: var(--ink);
  background: #ffffff;
  border: 1px solid var(--line);
}

.mode-button.active {
  color: white;
  background: var(--ink);
  border-color: var(--ink);
}

.mode-button:hover,
.ghost-button:hover,
.primary-button:hover,
.text-button:hover {
  transform: translateY(-1px);
}

.practice-layout {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(260px, 330px);
  gap: 18px;
  align-items: stretch;
}

.question-panel,
.lesson-panel,
.result-panel {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: var(--shadow);
}

.question-panel {
  display: flex;
  flex-direction: column;
  gap: 18px;
  min-height: 620px;
  padding: clamp(18px, 3vw, 30px);
}

.question-head {
  display: flex;
  align-items: start;
  justify-content: space-between;
  gap: 16px;
}

.topic-pill {
  display: inline-flex;
  align-items: center;
  min-height: 32px;
  padding: 0 12px;
  color: white;
  background: var(--teal);
  border-radius: 999px;
  font-weight: 800;
}

#questionMeta {
  margin: 8px 0 0;
  color: var(--muted);
}

.score-box {
  min-width: 78px;
  padding: 9px 12px;
  text-align: center;
  background: #fff7e8;
  border: 1px solid #f0cf92;
  border-radius: 8px;
}

.score-box strong {
  display: block;
  color: var(--gold);
  font-size: 1.8rem;
  line-height: 1;
}

.score-box span {
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 800;
}

.progress-track {
  height: 10px;
  overflow: hidden;
  background: #e8eef2;
  border-radius: 999px;
}

.progress-track span {
  display: block;
  width: 0%;
  height: 100%;
  background: linear-gradient(90deg, var(--teal), var(--coral), var(--gold));
  transition: width 220ms ease;
}

.prompt-area {
  display: grid;
  gap: 10px;
}

.instruction {
  margin: 0;
  color: var(--muted);
  font-weight: 800;
}

.prompt-area h3 {
  margin: 0;
  font-size: clamp(1.5rem, 4vw, 2.7rem);
  line-height: 1.16;
  letter-spacing: 0;
}

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

.option-button {
  min-height: 78px;
  padding: 14px 16px;
  color: var(--ink);
  text-align: left;
  background: #ffffff;
  border: 2px solid var(--line);
  border-radius: 8px;
  cursor: pointer;
}

.option-button:hover,
.option-button:focus-visible,
.option-button.selected {
  border-color: var(--cyan);
  outline: none;
  box-shadow: 0 0 0 3px rgba(29, 119, 149, 0.14);
}

.option-button.correct {
  border-color: var(--green);
  background: #eef9ef;
}

.option-button.incorrect {
  border-color: var(--coral);
  background: #fff0ef;
}

.option-letter {
  display: inline-grid;
  width: 26px;
  height: 26px;
  margin-right: 9px;
  place-items: center;
  color: white;
  background: var(--ink);
  border-radius: 6px;
  font-size: 0.8rem;
  font-weight: 900;
}

.feedback {
  padding: 14px 16px;
  background: #f4f7fa;
  border-left: 5px solid var(--cyan);
  border-radius: 8px;
}

.feedback.good {
  border-left-color: var(--green);
  background: #eef9ef;
}

.feedback.needs-work {
  border-left-color: var(--coral);
  background: #fff0ef;
}

.feedback strong {
  display: block;
  margin-bottom: 4px;
}

.feedback p {
  margin: 0;
  color: var(--muted);
  line-height: 1.55;
}

.question-actions {
  display: flex;
  gap: 10px;
  margin-top: auto;
}

.primary-button,
.ghost-button,
.text-button {
  border: 0;
  font-weight: 900;
}

.primary-button {
  padding: 0 18px;
  color: white;
  background: var(--teal);
  box-shadow: 0 12px 24px rgba(8, 127, 122, 0.22);
}

.ghost-button {
  padding: 0 16px;
  color: var(--ink);
  background: #e9eef2;
}

.text-button {
  width: 100%;
  color: var(--coral);
  background: #fff0ef;
}

.lesson-panel {
  display: flex;
  flex-direction: column;
  gap: 18px;
  padding: 18px;
}

.lesson-visual {
  position: relative;
  min-height: 160px;
  overflow: hidden;
  background:
    linear-gradient(135deg, rgba(8, 127, 122, 0.14), rgba(212, 81, 76, 0.12)),
    #edf6f7;
  border: 1px solid #cce3e4;
  border-radius: 8px;
}

.paper-card {
  position: absolute;
  display: grid;
  place-items: center;
  background: #ffffff;
  border: 2px solid rgba(23, 32, 38, 0.14);
  border-radius: 8px;
  box-shadow: 0 16px 26px rgba(23, 32, 38, 0.12);
}

.paper-main {
  left: 28px;
  top: 30px;
  width: 190px;
  height: 104px;
  grid-template-columns: 1fr;
  gap: 6px;
  padding: 14px;
  transform: rotate(-3deg);
}

.paper-main span {
  display: block;
  width: 100%;
  padding: 4px 8px;
  color: #ffffff;
  background: var(--teal);
  border-radius: 6px;
  font-weight: 900;
}

.paper-main span:nth-child(2) {
  background: var(--coral);
}

.paper-main span:nth-child(3) {
  background: var(--violet);
}

.paper-small {
  right: 28px;
  bottom: 24px;
  width: 64px;
  height: 64px;
  color: var(--gold);
  font-size: 2rem;
  font-weight: 900;
  transform: rotate(7deg);
}

.mini-lesson {
  display: grid;
  gap: 10px;
}

.mini-lesson p {
  margin: 0;
  color: var(--muted);
  line-height: 1.55;
}

.mini-lesson ul {
  display: grid;
  gap: 8px;
  margin: 0;
  padding-left: 18px;
  color: var(--ink);
}

.result-panel {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
  padding: 22px;
}

.result-panel p {
  margin: 6px 0 0;
  color: var(--muted);
}

.source-note {
  color: var(--muted);
  font-size: 0.78rem;
  line-height: 1.45;
}

.hidden {
  display: none !important;
}

@media (max-width: 980px) {
  .app-shell {
    grid-template-columns: 1fr;
  }

  .sidebar {
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }

  .topic-list {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .practice-layout {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 680px) {
  .sidebar,
  .workspace {
    padding: 16px;
  }

  .topbar,
  .result-panel {
    align-items: stretch;
    flex-direction: column;
  }

  .mode-controls {
    justify-content: stretch;
  }

  .mode-button {
    flex: 1 1 30%;
  }

  .topic-list,
  .options-grid {
    grid-template-columns: 1fr;
  }

  .question-panel {
    min-height: auto;
  }

  .question-actions {
    flex-direction: column;
  }

  .primary-button,
  .ghost-button {
    width: 100%;
  }
}