:root {
  --bg: #f5f6f8;
  --panel: #ffffff;
  --ink: #111827;
  --muted: #687385;
  --line: #d9e0ea;
  --soft: #eef2f7;
  --dark: #1f2937;
  --blue: #255f99;
  --good: #0f766e;
  --bad: #b42318;
  --warn: #805600;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  background: var(--bg);
  color: var(--ink);
  font-family: Arial, "Noto Sans SC", "PingFang SC", sans-serif;
}

button, textarea { font: inherit; }

.shell {
  width: min(1500px, 100%);
  margin: 0 auto;
  padding: 22px;
}

.top {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 300px;
  gap: 18px;
  margin-bottom: 18px;
}

.eyebrow {
  margin: 0 0 8px;
  color: var(--blue);
  font-size: 13px;
  font-weight: 800;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

h1 {
  margin: 0 0 8px;
  font-size: 42px;
  letter-spacing: 0;
}

h2 { margin: 0 0 12px; }

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

.page-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 16px;
}

.page-nav a {
  min-height: 36px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0 12px;
  border: 1px solid var(--line);
  border-radius: 7px;
  background: #fff;
  color: var(--ink);
  text-decoration: none;
  font-size: 14px;
  font-weight: 800;
}

.page-nav a:hover {
  background: var(--soft);
}

.score,
.problem-list,
.workspace,
.reference {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: 0 12px 28px rgba(15, 23, 42, 0.05);
}

.score {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 10px;
  padding: 14px;
}

.score div {
  border: 1px solid var(--line);
  border-radius: 7px;
  padding: 10px;
}

.score span {
  display: block;
  color: var(--muted);
  font-size: 13px;
}

.score strong {
  display: block;
  margin-top: 4px;
  font-size: 20px;
}

.score button { grid-column: 1 / -1; }

.grid {
  display: grid;
  grid-template-columns: 310px minmax(0, 1fr) 340px;
  gap: 18px;
  align-items: start;
}

.problem-list,
.reference {
  padding: 14px;
  position: sticky;
  top: 14px;
}

.problem-button {
  width: 100%;
  display: grid;
  grid-template-columns: 34px minmax(0, 1fr);
  gap: 10px;
  min-height: 70px;
  border: 0;
  border-radius: 7px;
  background: transparent;
  text-align: left;
  padding: 10px;
  cursor: pointer;
}

.problem-button:hover { background: var(--soft); }
.problem-button.active { background: var(--dark); color: #fff; }

.num {
  width: 30px;
  height: 30px;
  display: grid;
  place-items: center;
  border-radius: 999px;
  background: var(--soft);
  color: var(--ink);
  font-weight: 800;
}

.problem-button.done .num {
  background: #dff7f3;
  color: #064e3b;
}

.problem-meta {
  display: block;
  margin-top: 4px;
  color: var(--muted);
  font-size: 12px;
}

.problem-button.active .problem-meta { color: #d1d5db; }

.workspace {
  padding: 20px;
  min-width: 0;
}

.meta-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: 12px;
}

.pill {
  display: inline-flex;
  align-items: center;
  min-height: 28px;
  border-radius: 999px;
  padding: 4px 10px;
  background: var(--dark);
  color: #fff;
  font-size: 13px;
  font-weight: 800;
}

.pill.light {
  background: var(--soft);
  color: var(--muted);
}

#prompt {
  color: #374151;
  line-height: 1.65;
}

.toolbar,
.actions {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 14px 0;
}

button {
  min-height: 38px;
  border: 1px solid var(--line);
  border-radius: 7px;
  background: #fff;
  color: var(--ink);
  padding: 8px 12px;
  cursor: pointer;
}

button:hover { background: var(--soft); }

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

textarea {
  width: 100%;
  min-height: 330px;
  resize: vertical;
  border: 1px solid #c7d0dd;
  border-radius: 8px;
  padding: 14px;
  background: #0f172a;
  color: #f8fafc;
  line-height: 1.55;
  font-family: Consolas, "SFMono-Regular", Menlo, monospace;
  font-size: 14px;
}

.feedback {
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 14px;
  line-height: 1.55;
}

.feedback.good {
  border-color: #9bd8cf;
  background: #ecfdf9;
  color: #064e3b;
}

.feedback.bad {
  border-color: #f1b5af;
  background: #fff1f0;
  color: #7a271a;
}

.feedback.warn {
  border-color: #f1d38a;
  background: #fffbeb;
  color: #6b4200;
}

pre {
  margin: 0 0 14px;
  padding: 12px;
  overflow-x: auto;
  border-radius: 7px;
  background: #111827;
  color: #f8fafc;
  line-height: 1.5;
  font-size: 13px;
}

code, textarea {
  font-family: Consolas, "SFMono-Regular", Menlo, monospace;
}

.reference ul {
  margin: 0 0 16px;
  padding-left: 20px;
  color: #374151;
  line-height: 1.55;
}

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

.chips span {
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 5px 9px;
  background: var(--soft);
  font-size: 13px;
}

@media (max-width: 1150px) {
  .top, .grid { grid-template-columns: 1fr; }
  .problem-list, .reference { position: static; }
}