:root {
  --ink: #17201b;
  --muted: #66736d;
  --line: #dce6df;
  --paper: #f7faf7;
  --panel: #ffffff;
  --green: #0f8f65;
  --blue: #2d6cdf;
  --gold: #b57916;
  --rose: #c24a63;
  font-family: "Inter", "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
}

* { box-sizing: border-box; }
body {
  margin: 0;
  color: var(--ink);
  background: var(--paper);
}
a { color: inherit; text-decoration: none; }

.topbar {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  min-height: 72px;
  padding: 14px clamp(18px, 4vw, 56px);
  background: rgba(247, 250, 247, .92);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(14px);
}
.brand { display: flex; align-items: center; gap: 12px; }
.brand-mark {
  display: grid;
  place-items: center;
  width: 42px;
  height: 42px;
  color: #fff;
  background: var(--green);
  border-radius: 8px;
  font-weight: 800;
}
.brand strong, .brand small { display: block; }
.brand small { color: var(--muted); font-size: 12px; margin-top: 2px; }
.topbar nav { display: flex; gap: 18px; color: var(--muted); font-size: 14px; }

.app-layout {
  display: grid;
  grid-template-columns: minmax(300px, 440px) minmax(0, 1fr);
  gap: 24px;
  min-height: calc(100vh - 73px);
  padding: clamp(18px, 4vw, 56px);
}
.intro-panel, .chat-panel, .checkout-card, .pay-note {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 8px;
}
.intro-panel {
  align-self: start;
  padding: clamp(24px, 4vw, 42px);
}
.eyebrow {
  margin: 0 0 12px;
  color: var(--green);
  text-transform: uppercase;
  font-size: 12px;
  font-weight: 800;
}
h1, h2, h3, p { margin-top: 0; }
h1 { font-size: clamp(32px, 5vw, 56px); line-height: 1.05; letter-spacing: 0; }
.intro-panel p { color: var(--muted); line-height: 1.8; }
.quick-topics { display: grid; gap: 10px; margin: 26px 0; }
.quick-topics button {
  width: 100%;
  padding: 14px 16px;
  text-align: left;
  color: var(--ink);
  background: #eef7f1;
  border: 1px solid #cfe6d8;
  border-radius: 8px;
  cursor: pointer;
}
.credit-strip {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 14px;
  background: #fff7e8;
  border: 1px solid #eed6a8;
  border-radius: 8px;
  color: #6d4b12;
}
.credit-strip a { font-weight: 800; color: var(--gold); }

.chat-panel {
  display: flex;
  flex-direction: column;
  min-height: 680px;
  overflow: hidden;
}
.chat-header {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  padding: 18px 20px;
  border-bottom: 1px solid var(--line);
}
.chat-header span { display: block; color: var(--muted); font-size: 13px; margin-top: 4px; }
.chat-header a { color: var(--blue); font-weight: 700; }
.messages {
  flex: 1;
  overflow-y: auto;
  padding: 22px;
}
.message {
  max-width: 78%;
  margin-bottom: 16px;
  padding: 14px 16px;
  border-radius: 8px;
  line-height: 1.75;
  white-space: pre-wrap;
}
.message p { margin: 0; }
.message.assistant { background: #eef4ff; border: 1px solid #d5e2ff; }
.message.user {
  margin-left: auto;
  color: #fff;
  background: var(--green);
}
.composer {
  padding: 18px;
  border-top: 1px solid var(--line);
  background: #fbfdfb;
}
.composer textarea {
  width: 100%;
  resize: vertical;
  min-height: 104px;
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: 8px;
  font: inherit;
}
.composer-actions, .pay-actions {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-top: 12px;
}
.composer-actions span, .muted { color: var(--muted); font-size: 13px; }
button, .button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 42px;
  padding: 0 18px;
  border: 0;
  border-radius: 8px;
  font-weight: 800;
  cursor: pointer;
}
.composer button, .button.primary { color: #fff; background: var(--green); }
.button.secondary { color: #fff; background: var(--blue); }

.lab-section, .pay-page {
  padding: clamp(28px, 5vw, 64px) clamp(18px, 4vw, 56px);
}
.section-title { max-width: 720px; }
.section-title h2, .pay-hero h1 { font-size: clamp(28px, 4vw, 44px); }
.lab-grid, .pricing-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 18px;
  margin-top: 22px;
}
.lab-grid article, .price-card {
  padding: 24px;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 8px;
}
.lab-grid p, .pay-hero p, .price-card p, .price-card li, .pay-note p { color: var(--muted); line-height: 1.75; }

.pay-hero { max-width: 760px; }
.price-card { display: flex; flex-direction: column; justify-content: space-between; gap: 18px; }
.plan-name { color: var(--green) !important; font-weight: 800; }
.price-card h2 { font-size: 36px; margin-bottom: 6px; }
.validity { color: var(--gold) !important; font-weight: 800; }
.price-card ul { padding-left: 18px; margin: 0; }
.pay-note { margin-top: 24px; padding: 24px; }
.endpoint-list { display: grid; gap: 10px; }
.endpoint-list code {
  display: block;
  padding: 12px;
  overflow-x: auto;
  background: #f0f4f2;
  border-radius: 8px;
}

.checkout {
  display: grid;
  place-items: center;
  min-height: 100vh;
  padding: 24px;
}
.checkout-card { width: min(620px, 100%); padding: clamp(24px, 4vw, 44px); }
.checkout-price { font-size: 42px; color: var(--green); font-weight: 900; }
.checkout dl { display: grid; gap: 12px; margin: 22px 0; }
.checkout dl div { display: flex; justify-content: space-between; gap: 12px; padding: 12px 0; border-bottom: 1px solid var(--line); }
.checkout dt { color: var(--muted); }
.checkout dd { margin: 0; font-weight: 700; }
.back-link { color: var(--blue); margin-bottom: 16px; }

.footer {
  display: flex;
  flex-wrap: wrap;
  gap: 18px;
  padding: 24px clamp(18px, 4vw, 56px);
  color: var(--muted);
  border-top: 1px solid var(--line);
}
.footer span { color: var(--ink); font-weight: 800; }

@media (max-width: 880px) {
  .topbar { align-items: flex-start; flex-direction: column; }
  .topbar nav { flex-wrap: wrap; }
  .app-layout, .lab-grid, .pricing-grid { grid-template-columns: 1fr; }
  .chat-panel { min-height: 620px; }
  .message { max-width: 94%; }
  .pay-actions, .composer-actions { align-items: stretch; flex-direction: column; }
  .pay-actions .button, .composer button { width: 100%; }
}