:root {
  --ink: #17211c;
  --muted: #53635b;
  --line: #d7dfda;
  --bg: #f7f8f5;
  --panel: #ffffff;
  --accent: #0f6f5c;
  --accent-dark: #08483c;
  --accent-soft: #e4f3ee;
  --warn: #7a4f00;
  --bad: #9d1c27;
  --good: #11683e;
  --focus: #1f77b4;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: Inter, "Segoe UI", Arial, sans-serif;
  color: var(--ink);
  background: var(--bg);
  line-height: 1.55;
}

a { color: var(--accent-dark); }

.topbar {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 320px;
  gap: 24px;
  padding: 28px 32px;
  color: #fff;
  background:
    linear-gradient(90deg, rgba(9, 72, 59, 0.92), rgba(20, 56, 91, 0.88)),
    url("https://cdn.gradual.com/images/https://d2xo500swnpgl1.cloudfront.net/uploads/oaiacademy/Codex-for-Builders-1754586349827.png?width=1600");
  background-size: cover;
  background-position: center;
}

.eyebrow {
  margin: 0 0 8px;
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0;
  text-transform: uppercase;
}

h1, h2, h3 { line-height: 1.18; letter-spacing: 0; }
h1 { margin: 0; font-size: 42px; }
h2 { margin-top: 0; font-size: 30px; }
h3 { margin-top: 30px; font-size: 20px; }

.subtitle {
  max-width: 900px;
  margin: 12px 0 0;
  font-size: 18px;
}

.source-card {
  align-self: end;
  display: grid;
  gap: 6px;
  padding: 16px;
  border: 1px solid rgba(255,255,255,0.45);
  background: rgba(0,0,0,0.28);
  border-radius: 8px;
}

.source-card span,
.source-card small { color: rgba(255,255,255,0.82); }
.source-card a { color: #fff; font-weight: 700; }

.layout {
  display: grid;
  grid-template-columns: 280px minmax(0, 1fr);
  min-height: calc(100vh - 190px);
}

.sidebar {
  border-right: 1px solid var(--line);
  background: #eef2ef;
  padding: 18px;
}

.tabs {
  display: flex;
  gap: 8px;
}

.tabs.vertical {
  flex-direction: column;
  position: sticky;
  top: 18px;
}

button {
  min-height: 38px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: #fff;
  color: var(--ink);
  font: inherit;
  cursor: pointer;
}

button:hover { border-color: var(--accent); }
button:focus-visible, select:focus-visible, input:focus-visible {
  outline: 3px solid rgba(31,119,180,0.28);
  outline-offset: 2px;
}

.tab-btn {
  width: 100%;
  padding: 10px 12px;
  text-align: left;
  font-weight: 650;
}

.tab-btn.active,
.subtab-btn.active {
  color: #fff;
  border-color: var(--accent);
  background: var(--accent);
}

.workspace {
  min-width: 0;
  padding: 22px 28px 40px;
}

.voice-panel {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 16px;
  padding: 12px;
  margin-bottom: 18px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
}

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

.voice-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  justify-content: flex-end;
}

select {
  min-height: 38px;
  max-width: 260px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: #fff;
  color: var(--ink);
}

.panel { display: none; }
.panel.active { display: block; }

.lesson-content,
.quiz {
  max-width: 1120px;
  padding: 26px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  box-shadow: 0 10px 28px rgba(25, 40, 33, 0.05);
}

.subtabs {
  display: flex;
  gap: 8px;
  margin-bottom: 12px;
}

.subtab-btn {
  min-width: 110px;
  padding: 8px 14px;
  font-weight: 700;
}

.subpanel { display: none; }
.subpanel.active { display: block; }

.workflow-map {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
  margin: 24px 0;
}

.workflow-map details {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
  overflow: hidden;
}

.workflow-map summary {
  min-height: 104px;
  display: grid;
  align-content: center;
  gap: 6px;
  padding: 16px;
  border-left: 5px solid var(--accent);
  background: var(--accent-soft);
  cursor: pointer;
}

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

.workflow-map summary::after {
  content: "Open details";
  display: inline-block;
  width: max-content;
  margin-top: 6px;
  padding: 4px 8px;
  border: 1px solid rgba(15,111,92,0.24);
  border-radius: 6px;
  color: var(--accent-dark);
  background: #fff;
  font-size: 12px;
  font-weight: 800;
}

.workflow-map details[open] summary::after {
  content: "Close details";
}

.workflow-map summary span {
  display: block;
  font-size: 20px;
  font-weight: 850;
}

.workflow-map summary small {
  color: var(--muted);
  font-size: 14px;
}

.workflow-map details > div {
  padding: 18px;
}

.workflow-map details > div p:first-child { margin-top: 0; }
.workflow-map details > div ul { margin-bottom: 0; }

.terms {
  display: grid;
  grid-template-columns: 190px minmax(0, 1fr);
  gap: 10px 16px;
}

.terms dt { font-weight: 800; }
.terms dd { margin: 0; }

table {
  width: 100%;
  border-collapse: collapse;
  margin: 18px 0;
}

th, td {
  padding: 12px;
  border: 1px solid var(--line);
  vertical-align: top;
}

th {
  text-align: left;
  background: #edf4f1;
}

pre {
  overflow-x: auto;
  padding: 16px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #f2f5f3;
}

code {
  font-family: "Cascadia Mono", Consolas, monospace;
  font-size: 0.94em;
}

.quiz-header {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  align-items: center;
  margin-bottom: 18px;
}

.quiz-header h2 { margin: 0; }

.score {
  min-width: 120px;
  padding: 8px 12px;
  border-radius: 6px;
  background: var(--accent-soft);
  font-weight: 800;
  text-align: center;
}

.question-card {
  padding: 18px;
  margin: 16px 0;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
}

.question-card h3 {
  margin: 0 0 12px;
  font-size: 18px;
}

.option {
  display: flex;
  gap: 10px;
  align-items: flex-start;
  padding: 10px;
  margin: 8px 0;
  border: 1px solid var(--line);
  border-radius: 6px;
  cursor: pointer;
}

.option:hover { background: #f6fbf9; }
.option input { margin-top: 5px; }

.feedback {
  display: none;
  margin-top: 14px;
  padding: 14px;
  border-radius: 8px;
  background: #f7f8f5;
  border: 1px solid var(--line);
}

.feedback.visible { display: block; }
.feedback.correct { border-left: 5px solid var(--good); }
.feedback.incorrect { border-left: 5px solid var(--bad); }

.feedback strong { display: block; margin-bottom: 8px; }
.feedback ul { margin: 8px 0 0; }

@media (max-width: 920px) {
  .topbar,
  .layout {
    grid-template-columns: 1fr;
  }
  .sidebar {
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }
  .tabs.vertical {
    position: static;
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
  .voice-panel {
    align-items: flex-start;
    flex-direction: column;
  }
  .voice-actions { justify-content: flex-start; }
  .workflow-map { grid-template-columns: 1fr; }
}

@media (max-width: 560px) {
  h1 { font-size: 32px; }
  .workspace { padding: 16px; }
  .lesson-content, .quiz { padding: 18px; }
  .tabs.vertical,
  .workflow-map,
  .terms {
    grid-template-columns: 1fr;
  }
  .quiz-header { align-items: flex-start; flex-direction: column; }
}