:root {
  color-scheme: light;
  --bg: oklch(0.97 0.018 87);
  --bg-soft: oklch(0.94 0.026 82);
  --paper: oklch(0.99 0.01 95 / 0.92);
  --paper-strong: oklch(0.985 0.012 90);
  --ink: oklch(0.25 0.03 40);
  --muted: oklch(0.48 0.03 52);
  --line: oklch(0.86 0.03 80);
  --accent: oklch(0.57 0.15 42);
  --accent-soft: oklch(0.93 0.05 45);
  --accent-2: oklch(0.45 0.08 200);
  --shadow: 0 24px 60px oklch(0.45 0.05 40 / 0.12);
  --radius-xl: 32px;
  --radius-lg: 22px;
  --radius-md: 16px;
  --radius-sm: 12px;
  --transition: 220ms cubic-bezier(0.22, 1, 0.36, 1);
  --content-width: 1480px;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: "Noto Serif SC", "Songti SC", "STSong", "Source Han Serif SC", serif;
  color: var(--ink);
  background:
    radial-gradient(circle at top left, oklch(0.92 0.06 55 / 0.9), transparent 24rem),
    radial-gradient(circle at top right, oklch(0.9 0.04 190 / 0.75), transparent 26rem),
    linear-gradient(180deg, var(--bg), oklch(0.955 0.014 88));
}

body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  background:
    linear-gradient(90deg, transparent 0 8%, oklch(1 0 0 / 0.22) 8% 8.15%, transparent 8.15% 100%),
    linear-gradient(transparent 0 96%, oklch(0.7 0.02 82 / 0.06) 96% 100%);
  background-size: 100% 100%, 100% 14px;
  mix-blend-mode: multiply;
  opacity: 0.5;
}

.page-shell {
  width: min(calc(100% - 2rem), var(--content-width));
  margin: 0 auto;
  padding: clamp(1.2rem, 2vw, 2rem) 0 3rem;
}

.hero {
  position: relative;
  display: grid;
  grid-template-columns: minmax(0, 1.5fr) minmax(18rem, 0.9fr);
  gap: 1.25rem;
  margin-bottom: 1.5rem;
  padding: clamp(1.4rem, 2.4vw, 2.4rem);
  border: 1px solid oklch(0.86 0.03 75 / 0.9);
  border-radius: var(--radius-xl);
  background:
    linear-gradient(135deg, oklch(1 0.01 90 / 0.92), oklch(0.975 0.02 80 / 0.95)),
    var(--paper);
  box-shadow: var(--shadow);
  overflow: hidden;
}

.hero::after {
  content: "";
  position: absolute;
  inset: auto -3rem -4rem auto;
  width: 18rem;
  height: 18rem;
  border-radius: 50%;
  background: radial-gradient(circle, oklch(0.92 0.06 45 / 0.9), transparent 72%);
  filter: blur(4px);
}

.eyebrow,
.panel-label,
.toolbar-label {
  margin: 0 0 0.45rem;
  font-size: 0.78rem;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--muted);
}

.hero h1 {
  margin: 0;
  max-width: 10ch;
  font-size: clamp(2.4rem, 5vw, 4.6rem);
  line-height: 0.94;
  letter-spacing: -0.05em;
}

.hero-text {
  max-width: 38rem;
  margin: 1rem 0 0;
  font-size: 1rem;
  line-height: 1.8;
  color: color-mix(in oklab, var(--ink) 78%, var(--muted));
}

.hero-stats {
  position: relative;
  z-index: 1;
  display: grid;
  gap: 0.9rem;
  align-content: start;
}

.hero-stat {
  padding: 1rem 1rem 0.95rem;
  border: 1px solid oklch(0.84 0.025 82 / 0.95);
  border-radius: var(--radius-lg);
  background: color-mix(in oklab, var(--paper) 88%, white);
}

.hero-stat strong {
  display: block;
  margin-bottom: 0.25rem;
  font-size: 2rem;
  font-weight: 600;
  letter-spacing: -0.04em;
}

.hero-stat span {
  color: var(--muted);
  font-size: 0.95rem;
}

.workspace {
  display: grid;
  grid-template-columns: minmax(17rem, 22rem) minmax(0, 1fr);
  gap: 1.2rem;
  align-items: start;
}

.sidebar,
.content {
  min-width: 0;
}

.sidebar {
  position: sticky;
  top: 1rem;
  display: grid;
  gap: 1rem;
}

.panel,
.toolbar,
.question-card,
.result-summary {
  border: 1px solid oklch(0.86 0.03 80 / 0.96);
  border-radius: var(--radius-lg);
  background: var(--paper);
  box-shadow: 0 14px 40px oklch(0.5 0.03 48 / 0.08);
}

.panel {
  padding: 1rem;
}

.panel-heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.8rem;
  margin-bottom: 0.7rem;
}

.clear-button {
  border: 0;
  background: none;
  color: var(--accent-2);
  font: inherit;
  cursor: pointer;
}

.category-tabs,
.paper-list,
.question-list {
  display: grid;
  gap: 0.7rem;
}

.tab-button,
.paper-button {
  width: 100%;
  border: 1px solid var(--line);
  border-radius: var(--radius-md);
  background: color-mix(in oklab, var(--paper-strong) 95%, white);
  color: var(--ink);
  cursor: pointer;
  transition:
    transform var(--transition),
    border-color var(--transition),
    background var(--transition),
    box-shadow var(--transition);
}

.tab-button:hover,
.paper-button:hover,
.tab-button:focus-visible,
.paper-button:focus-visible {
  transform: translateY(-1px);
  border-color: color-mix(in oklab, var(--accent) 45%, var(--line));
  outline: none;
}

.tab-button {
  padding: 0.95rem 1rem;
  text-align: left;
}

.tab-button strong,
.paper-button strong {
  display: block;
  font-size: 1rem;
}

.tab-button span,
.paper-button span {
  display: block;
  margin-top: 0.25rem;
  color: var(--muted);
  font-size: 0.88rem;
}

.tab-button.active,
.paper-button.active {
  border-color: color-mix(in oklab, var(--accent) 60%, white);
  background:
    linear-gradient(135deg, var(--accent-soft), color-mix(in oklab, var(--paper) 80%, white));
  box-shadow: inset 0 0 0 1px oklch(0.82 0.05 52 / 0.75);
}

.paper-button {
  padding: 0.8rem 0.9rem;
  text-align: left;
}

.content {
  display: grid;
  gap: 0.9rem;
}

.toolbar {
  display: flex;
  flex-wrap: wrap;
  align-items: end;
  justify-content: space-between;
  gap: 1rem;
  padding: 1rem 1.1rem;
}

.toolbar h2 {
  margin: 0;
  font-size: clamp(1.55rem, 2vw, 2.1rem);
  letter-spacing: -0.04em;
}

.search-box {
  display: grid;
  gap: 0.35rem;
  min-width: min(100%, 19rem);
  color: var(--muted);
  font-size: 0.9rem;
}

.search-box input {
  width: 100%;
  padding: 0.85rem 0.95rem;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: color-mix(in oklab, white 62%, var(--paper));
  color: var(--ink);
  font: inherit;
}

.search-box input:focus-visible {
  outline: 2px solid color-mix(in oklab, var(--accent) 45%, white);
  outline-offset: 2px;
}

.result-summary {
  padding: 0.95rem 1.1rem;
  color: var(--muted);
  font-size: 0.96rem;
}

.question-card {
  position: relative;
  overflow: hidden;
}

.question-card::before {
  content: "";
  position: absolute;
  inset: 0 auto 0 0;
  width: 5px;
  background:
    linear-gradient(180deg, color-mix(in oklab, var(--accent) 82%, white), var(--accent-2));
}

.question-card-inner {
  padding: 1.15rem 1.15rem 1.2rem 1.35rem;
}

.meta-row,
.tag-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem;
}

.meta-row {
  margin-bottom: 0.9rem;
}

.meta-pill,
.tag-pill {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.35rem 0.7rem;
  border-radius: 999px;
  background: color-mix(in oklab, var(--accent-soft) 78%, white);
  color: color-mix(in oklab, var(--ink) 80%, var(--accent-2));
  font-size: 0.83rem;
}

.tag-pill {
  background: color-mix(in oklab, var(--paper-strong) 70%, var(--bg-soft));
}

.question-title {
  margin: 0 0 0.8rem;
  font-size: 1.25rem;
  line-height: 1.4;
}

.question-blocks,
.explanation-body,
.answer-box {
  display: grid;
  gap: 0.85rem;
}

.text-block,
.answer-box,
.explanation-body {
  color: color-mix(in oklab, var(--ink) 90%, var(--muted));
  line-height: 1.85;
}

.text-block {
  white-space: pre-wrap;
}

.latex-sup,
.latex-sub {
  line-height: 0;
}

.latex-underline,
.latex-wave {
  text-decoration-line: underline;
  text-decoration-thickness: 0.08em;
  text-underline-offset: 0.14em;
}

.latex-wave {
  text-decoration-style: wavy;
}

.latex-dotted {
  display: inline-flex;
  flex-wrap: wrap;
  gap: 0.02em;
}

.latex-dotted-char {
  position: relative;
  display: inline-block;
  padding-bottom: 0.28em;
}

.latex-dotted-char::after {
  content: "•";
  position: absolute;
  left: 50%;
  bottom: -0.14em;
  transform: translateX(-50%);
  font-size: 1.05em;
  line-height: 1;
  font-weight: 700;
}

.latex-underset {
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  line-height: 1.1;
  vertical-align: middle;
}

.latex-underset-note {
  font-size: 0.78em;
}

.figure {
  margin: 0;
  padding: 0.3rem;
  border-radius: var(--radius-md);
  background: color-mix(in oklab, var(--paper-strong) 90%, white);
}

.figure img {
  display: block;
  max-width: 100%;
  height: auto;
  border-radius: calc(var(--radius-md) - 4px);
}

.table-wrap {
  overflow-x: auto;
  border: 1px solid var(--line);
  border-radius: var(--radius-md);
  background: color-mix(in oklab, white 70%, var(--paper));
}

table {
  width: 100%;
  border-collapse: collapse;
  min-width: 32rem;
}

th,
td {
  padding: 0.8rem 0.9rem;
  border-bottom: 1px solid color-mix(in oklab, var(--line) 82%, white);
  text-align: left;
  vertical-align: top;
  line-height: 1.7;
}

th {
  background: color-mix(in oklab, var(--accent-soft) 62%, white);
  font-weight: 600;
}

.options {
  display: grid;
  gap: 0.55rem;
  margin: 0.95rem 0 0;
  padding: 0;
  list-style: none;
}

.subquestion-stem {
  margin-top: 1.15rem;
  font-size: 1.02rem;
  font-weight: 600;
  line-height: 1.75;
  color: color-mix(in oklab, var(--ink) 92%, var(--muted));
}

.choice-group {
  display: grid;
  gap: 0.75rem;
}

.option-item {
  display: block;
}

.option-static {
  display: grid;
  grid-template-columns: 2rem minmax(0, 1fr);
  gap: 0.7rem;
  padding: 0.75rem 0.85rem;
  border: 1px solid color-mix(in oklab, var(--line) 92%, white);
  border-radius: var(--radius-md);
  background: color-mix(in oklab, white 72%, var(--paper));
}

.option-choice {
  width: 100%;
  display: grid;
  grid-template-columns: 2rem minmax(0, 1fr);
  gap: 0.7rem;
  padding: 0.75rem 0.85rem;
  border: 1px solid color-mix(in oklab, var(--line) 92%, white);
  border-radius: var(--radius-md);
  background: color-mix(in oklab, white 72%, var(--paper));
  color: inherit;
  text-align: left;
  cursor: pointer;
  transition:
    transform var(--transition),
    border-color var(--transition),
    background var(--transition),
    box-shadow var(--transition);
}

.option-choice:hover,
.option-choice:focus-visible {
  transform: translateY(-1px);
  border-color: color-mix(in oklab, var(--accent) 40%, var(--line));
  outline: none;
}

.option-choice.is-selected {
  border-color: color-mix(in oklab, var(--accent) 55%, white);
  background: color-mix(in oklab, var(--accent-soft) 52%, white);
}

.option-choice.is-correct {
  border-color: oklch(0.68 0.13 145);
  background: oklch(0.96 0.05 145);
}

.option-choice.is-incorrect {
  border-color: oklch(0.67 0.16 25);
  background: oklch(0.96 0.04 25);
}

.option-label {
  display: inline-grid;
  place-items: center;
  width: 2rem;
  height: 2rem;
  border-radius: 50%;
  background: color-mix(in oklab, var(--accent-soft) 78%, white);
  color: color-mix(in oklab, var(--ink) 78%, var(--accent-2));
  font-weight: 600;
}

.option-text {
  white-space: pre-wrap;
  line-height: 1.7;
}

.choice-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 0.8rem 1rem;
  padding: 0.1rem 0 0.35rem;
}

.choice-status {
  margin: 0;
  color: var(--muted);
  font-size: 0.94rem;
  line-height: 1.7;
}

.choice-action-buttons {
  display: flex;
  flex-wrap: wrap;
  gap: 0.6rem;
}

.choice-button {
  border: 0;
  border-radius: 999px;
  padding: 0.7rem 1rem;
  background: color-mix(in oklab, var(--accent) 82%, white);
  color: oklch(0.99 0.01 95);
  font: inherit;
  cursor: pointer;
  transition:
    transform var(--transition),
    opacity var(--transition),
    background var(--transition);
}

.choice-button:hover,
.choice-button:focus-visible {
  transform: translateY(-1px);
  outline: none;
}

.choice-button.secondary {
  background: color-mix(in oklab, var(--paper-strong) 82%, white);
  color: var(--ink);
  border: 1px solid color-mix(in oklab, var(--line) 92%, white);
}

.choice-button:disabled {
  cursor: not-allowed;
  opacity: 0.45;
  transform: none;
}

details.solution {
  margin-top: 1rem;
  border: 1px dashed color-mix(in oklab, var(--accent) 35%, var(--line));
  border-radius: var(--radius-md);
  background: color-mix(in oklab, var(--accent-soft) 38%, white);
}

details.solution[open] {
  border-style: solid;
}

details.solution summary {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 0.9rem 1rem;
  cursor: pointer;
  list-style: none;
  font-weight: 600;
}

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

.solution-content {
  display: grid;
  gap: 1rem;
  padding: 0 1rem 1rem;
}

.solution-title {
  margin: 0 0 0.45rem;
  font-size: 0.88rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
}

.empty-state {
  padding: 2.2rem 1.4rem;
  border: 1px dashed var(--line);
  border-radius: var(--radius-lg);
  background: color-mix(in oklab, white 58%, var(--paper));
}

.empty-state h3 {
  margin: 0 0 0.55rem;
  font-size: 1.3rem;
}

.empty-state p {
  margin: 0;
  color: var(--muted);
  line-height: 1.8;
}

@media (max-width: 1080px) {
  .hero,
  .workspace {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: static;
  }
}

@media (max-width: 720px) {
  .page-shell {
    width: min(calc(100% - 1rem), var(--content-width));
    padding-top: 0.6rem;
  }

  .hero {
    padding: 1.1rem;
    border-radius: 26px;
  }

  .hero h1 {
    max-width: none;
  }

  .question-card-inner,
  .toolbar,
  .panel,
  .result-summary {
    padding-left: 1rem;
    padding-right: 1rem;
  }

  .option-static,
  .option-choice {
    grid-template-columns: 1fr;
  }

  .option-label {
    width: 1.9rem;
    height: 1.9rem;
  }

  table {
    min-width: 26rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation: none !important;
    transition: none !important;
    scroll-behavior: auto !important;
  }
}