:root {
  --bg: #eef3f8;
  --panel: #ffffff;
  --chrome: #dce4ef;
  --ink: #0f172a;
  --muted: #64748b;
  --accent: #0b57d0;
  --accent-soft: #dbeafe;
  --line: #cbd5e1;
  --node: #f8fafc;
  --current: #dcfce7;
  --danger: #ef4444;
  --warn: #f59e0b;
  --ok: #10b981;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  font-family: "DM Sans", sans-serif;
  color: var(--ink);
  background:
    radial-gradient(circle at 10% 15%, #c7ddff 0%, transparent 30%),
    radial-gradient(circle at 90% 85%, #d1fae5 0%, transparent 25%),
    var(--bg);
  padding: 2rem;
}

.page-title {
  max-width: 1100px;
  margin: 0 auto 1rem;
}

.page-title h1 {
  margin: 0;
  font: 700 clamp(1.3rem, 2.5vw, 2rem) "Space Grotesk", sans-serif;
  color: #0b3a7e;
}

.lab-home {
  color: inherit;
  text-decoration: none;
}

.lab-home:hover {
  text-decoration: underline;
}

.app-shell {
  max-width: 1100px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: 1.35fr 1fr;
  gap: 1.25rem;
}

.app-shell.locked {
  opacity: 0.5;
  pointer-events: none;
  user-select: none;
}

.student-gate {
  max-width: 1100px;
  margin: 0 auto 1rem;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 16px;
  box-shadow: 0 12px 30px rgba(15, 23, 42, 0.08);
  padding: 1rem;
}

.student-gate h2 {
  margin: 0 0 0.35rem;
  font: 700 1.1rem "Space Grotesk", sans-serif;
}

.student-gate p {
  margin: 0 0 0.65rem;
  color: #334155;
  font-size: 0.92rem;
}

.student-form {
  display: flex;
  flex-wrap: wrap;
  align-items: end;
  gap: 0.6rem;
}

.student-form label {
  width: 100%;
  font-size: 0.85rem;
  color: #475569;
}

.student-form input {
  flex: 1;
  min-width: 220px;
  height: 40px;
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 0 0.7rem;
  font: 500 0.95rem "DM Sans", sans-serif;
}

.student-form button {
  height: 40px;
  border: 1px solid var(--accent);
  background: var(--accent);
  color: #fff;
  border-radius: 10px;
  padding: 0 0.9rem;
  font: 700 0.92rem "DM Sans", sans-serif;
  cursor: pointer;
}

.student-form button:disabled {
  opacity: 0.65;
  cursor: wait;
}

.gate-status {
  min-height: 1.15rem;
  margin-top: 0.45rem;
  font-size: 0.84rem;
}

.browser,
.panel {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 16px;
  box-shadow: 0 12px 30px rgba(15, 23, 42, 0.08);
  overflow: hidden;
}

.browser-top {
  display: flex;
  align-items: center;
  gap: 0.8rem;
  background: var(--chrome);
  border-bottom: 1px solid var(--line);
  padding: 0.75rem 1rem;
}

.window-controls {
  display: flex;
  gap: 0.4rem;
}

.dot {
  width: 12px;
  height: 12px;
  border-radius: 50%;
  display: inline-block;
}

.dot.red { background: var(--danger); }
.dot.yellow { background: var(--warn); }
.dot.green { background: var(--ok); }

.tab-strip { flex: 1; }

.tab {
  width: fit-content;
  background: #ffffff;
  border: 1px solid var(--line);
  border-bottom: 0;
  border-radius: 10px 10px 0 0;
  padding: 0.45rem 0.85rem;
  font-size: 0.9rem;
  font-weight: 500;
}

.toolbar {
  display: flex;
  align-items: center;
  gap: 0.65rem;
  padding: 0.85rem;
  border-bottom: 1px solid var(--line);
}

.tool-btn,
.go-btn {
  border: 1px solid var(--line);
  border-radius: 10px;
  background: #ffffff;
  color: var(--ink);
  font-size: 1rem;
  height: 38px;
  padding: 0 0.8rem;
  cursor: pointer;
}

.tool-btn:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

.go-btn {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
  font-weight: 700;
}

.url-wrap {
  flex: 1;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  border: 1px solid var(--line);
  background: #fff;
  border-radius: 999px;
  padding: 0 0.9rem;
  min-width: 0;
}

.lock {
  font-size: 0.9rem;
  color: var(--muted);
}

#urlInput {
  width: 100%;
  border: 0;
  outline: 0;
  height: 38px;
  font-size: 0.95rem;
  font-family: inherit;
}

.viewport {
  padding: 2.5rem 1.5rem;
  min-height: 300px;
  display: grid;
  align-content: center;
  justify-items: center;
  text-align: center;
  background: linear-gradient(180deg, #f8fbff, #ffffff);
}

.site-badge {
  background: var(--accent-soft);
  color: var(--accent);
  border: 1px solid #bfdbfe;
  border-radius: 999px;
  padding: 0.25rem 0.7rem;
  font-size: 0.78rem;
  letter-spacing: 0.03em;
  text-transform: uppercase;
  font-weight: 700;
}

#currentPage {
  margin: 0.8rem 0 0.35rem;
  font: 700 clamp(1.8rem, 4vw, 2.6rem) "Space Grotesk", sans-serif;
}

#pageHint {
  margin: 0;
  color: var(--muted);
}

.panel {
  padding: 1rem;
  display: flex;
  flex-direction: column;
  gap: 0.9rem;
}

.panel-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.8rem;
}

.panel-head h2 {
  margin: 0;
  font: 700 1.1rem "Space Grotesk", sans-serif;
}

.index-chip {
  font-size: 0.8rem;
  border-radius: 999px;
  background: #ecfeff;
  border: 1px solid #a5f3fc;
  padding: 0.25rem 0.65rem;
}

.history-list {
  border: 1px dashed var(--line);
  border-radius: 12px;
  padding: 0.75rem;
  min-height: 120px;
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem;
  align-content: flex-start;
}

.node {
  background: var(--node);
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 0.45rem 0.6rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.9rem;
}

.node.current {
  background: var(--current);
  border-color: #22c55e;
}

.arrow {
  color: #94a3b8;
  font-size: 1.05rem;
  align-self: center;
}

.legend {
  display: flex;
  gap: 1rem;
  font-size: 0.82rem;
  color: var(--muted);
}

.legend span {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
}

.swatch {
  width: 12px;
  height: 12px;
  border-radius: 3px;
  display: inline-block;
  border: 1px solid var(--line);
}

.swatch.current { background: var(--current); border-color: #22c55e; }
.swatch.node { background: var(--node); }

.commands {
  border-top: 1px solid var(--line);
  padding-top: 0.6rem;
}

.learning {
  border: 1px solid var(--line);
  border-radius: 12px;
  background: #f8fafc;
  padding: 0.75rem;
}

.learning h3 {
  margin: 0 0 0.4rem;
  font-size: 0.95rem;
}

#activitySummary {
  margin: 0 0 0.45rem;
  font-size: 0.88rem;
  color: #334155;
}

.step-checklist {
  margin: 0 0 0.6rem;
  padding-left: 1.1rem;
  font-size: 0.84rem;
  color: #1e293b;
}

.step-checklist li {
  margin: 0.2rem 0;
}

.node-table-wrap {
  border: 1px solid var(--line);
  border-radius: 10px;
  overflow: auto;
  background: #fff;
}

.node-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.8rem;
}

.node-table th,
.node-table td {
  border-bottom: 1px solid #e2e8f0;
  padding: 0.4rem 0.45rem;
  text-align: left;
  white-space: nowrap;
}

.node-table th {
  font-weight: 700;
  background: #f1f5f9;
}

.node-table tr:last-child td {
  border-bottom: 0;
}

.yes-current {
  color: #166534;
  font-weight: 700;
}

.commands h3 {
  margin: 0 0 0.4rem;
  font-size: 0.95rem;
}

#commandLog {
  margin: 0;
  padding-left: 1.15rem;
  font-size: 0.88rem;
  color: #1e293b;
  max-height: 180px;
  overflow: auto;
}

#commandLog li {
  margin: 0.22rem 0;
}

.page-footer {
  max-width: 1100px;
  margin: 1rem auto 0;
  font-size: 0.9rem;
  color: #334155;
}

.page-footer a {
  color: #0b57d0;
  text-decoration: none;
  font-weight: 700;
}

.page-footer a:hover {
  text-decoration: underline;
}

@media (max-width: 930px) {
  body { padding: 1rem; }

  .app-shell {
    grid-template-columns: 1fr;
  }

  .student-form button {
    width: 100%;
  }

  .toolbar {
    flex-wrap: wrap;
  }

  .url-wrap {
    width: 100%;
    order: 3;
  }

  .go-btn {
    order: 4;
    margin-left: auto;
  }
}