:root {
  --paper: #f4f5f8;
  --card: #ffffff;
  --ink: #2c2c2c;
  --muted: #63677a;
  --rule: #e3e5ed;
  --navy: #1b2a5e;
  --gold: #f0b432;
  --ok: #0d7a4a;
  --ok-bg: #e8f5ef;
  --bad: #c8102e;
  --bad-bg: #fdecef;
  --code-bg: #161b33;
  --mono: "SF Mono", Menlo, Consolas, "Courier New", monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "Helvetica Neue", Arial, sans-serif;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.55;
  color: var(--ink);
  background: var(--paper);
}

header {
  background: var(--navy);
  color: #fff;
  border-bottom: 3px solid var(--gold);
}

.header-inner {
  max-width: 1200px;
  margin: 0 auto;
  padding: 20px 24px;
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 16px;
  flex-wrap: wrap;
}

.eyebrow {
  margin: 0 0 6px;
  font-size: 11px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--gold);
  font-weight: 700;
}

h1 {
  margin: 0 0 8px;
  font-size: clamp(22px, 4vw, 28px);
  letter-spacing: 0.03em;
}

.sub { margin: 0; opacity: 0.9; font-size: 14px; max-width: 52ch; }

.loader-badge {
  font-size: 12px;
  padding: 8px 12px;
  border: 1px solid rgba(255,255,255,0.35);
  border-radius: 4px;
  white-space: nowrap;
}

.loader-badge.ready { border-color: var(--gold); color: var(--gold); }

.layout {
  max-width: 1320px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: 260px minmax(0, 1fr) 300px;
  gap: 0;
  min-height: calc(100vh - 120px);
}

@media (max-width: 1100px) {
  .layout { grid-template-columns: 260px 1fr; }
  .coach-panel { grid-column: 1 / -1; border-top: 1px solid var(--rule); max-height: 360px; }
}

@media (max-width: 800px) {
  .layout { grid-template-columns: 1fr; }
  .sidebar { border-right: none; border-bottom: 1px solid var(--rule); max-height: 220px; overflow: auto; }
  .coach-panel { max-height: none; }
}

.sidebar {
  background: var(--card);
  border-right: 1px solid var(--rule);
  padding: 12px 0;
  overflow-y: auto;
}

.unit-block { margin-bottom: 8px; }

.unit-label {
  padding: 8px 16px;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--navy);
}

.unit-block:nth-child(n+8) .unit-label {
  color: var(--label);
  padding-top: 14px;
  border-top: 1px solid var(--rule);
  margin-top: 8px;
}

.lesson-link {
  display: block;
  width: 100%;
  text-align: left;
  border: none;
  background: transparent;
  padding: 8px 16px 8px 20px;
  font: inherit;
  font-size: 14px;
  cursor: pointer;
  color: var(--ink);
  border-left: 3px solid transparent;
}

.lesson-link:hover { background: var(--paper); }

.lesson-link.active {
  background: var(--paper);
  border-left-color: var(--gold);
  font-weight: 600;
}

.lesson-link.done::after {
  content: " ✓";
  color: var(--ok);
  font-weight: 700;
}

.content { padding: 24px; }

.hidden { display: none !important; }

.welcome {
  background: var(--card);
  border: 1px solid var(--rule);
  padding: 24px;
  max-width: 640px;
}

.welcome .note {
  font-size: 14px;
  color: var(--muted);
  border-left: 3px solid var(--gold);
  padding-left: 12px;
}

.lesson-panel { max-width: 820px; }

.lesson-meta {
  display: flex;
  gap: 12px;
  align-items: center;
  margin-bottom: 8px;
  font-size: 13px;
  color: var(--muted);
}

.chip {
  background: var(--navy);
  color: #fff;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.1em;
  padding: 4px 10px;
  text-transform: uppercase;
}

#lessonTitle { margin: 0 0 16px; color: var(--navy); font-size: 22px; }

.instructions {
  background: var(--card);
  border: 1px solid var(--rule);
  padding: 16px 18px;
  margin-bottom: 16px;
}

.instructions p { margin: 0 0 10px; }
.instructions p:last-child { margin-bottom: 0; }
.instructions code {
  font-family: var(--mono);
  font-size: 0.9em;
  background: var(--paper);
  padding: 1px 5px;
  border-radius: 2px;
}

.editor-wrap {
  border: 1px solid var(--rule);
  background: var(--card);
}

.editor-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 8px 12px;
  font-size: 12px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--muted);
  border-bottom: 1px solid var(--rule);
}

#editor {
  width: 100%;
  min-height: 220px;
  border: none;
  resize: vertical;
  padding: 14px 16px;
  font-family: var(--mono);
  font-size: 14px;
  line-height: 1.5;
  background: var(--code-bg);
  color: #e9eaf2;
  tab-size: 4;
}

#editor:focus { outline: 2px solid var(--gold); outline-offset: -2px; }

.editor-hint {
  font-size: 12px;
  color: var(--muted);
  margin: 0 0 10px;
}

.actions {
  display: flex;
  gap: 10px;
  margin: 14px 0;
}

button {
  font: inherit;
  cursor: pointer;
  border-radius: 4px;
  padding: 10px 18px;
  border: none;
  font-weight: 600;
}

button:disabled { opacity: 0.5; cursor: not-allowed; }

.primary { background: var(--navy); color: #fff; }
.primary:hover:not(:disabled) { filter: brightness(1.08); }

.secondary { background: var(--card); color: var(--navy); border: 2px solid var(--navy); }
.ghost { background: transparent; color: var(--navy); border: 1px solid var(--rule); padding: 6px 12px; font-size: 13px; }

.output-panel {
  background: var(--card);
  border: 1px solid var(--rule);
  padding: 12px 16px;
  margin-bottom: 12px;
}

.output-panel h3 { margin: 0 0 8px; font-size: 13px; text-transform: uppercase; letter-spacing: 0.08em; color: var(--muted); }

#runOutput {
  margin: 0;
  font-family: var(--mono);
  font-size: 13px;
  white-space: pre-wrap;
  background: var(--paper);
  padding: 10px;
  min-height: 2em;
}

.feedback {
  border-radius: 4px;
  padding: 14px 16px;
  margin-bottom: 16px;
  font-size: 15px;
}

.feedback.pass { background: var(--ok-bg); border-left: 4px solid var(--ok); }
.feedback.fail { background: var(--bad-bg); border-left: 4px solid var(--bad); }

.feedback h3 { margin: 0 0 8px; font-size: 16px; }
.feedback pre {
  margin: 8px 0 0;
  font-family: var(--mono);
  font-size: 12px;
  white-space: pre-wrap;
  background: rgba(0,0,0,0.05);
  padding: 10px;
}

.feedback ul { margin: 8px 0 0; padding-left: 20px; }

.lesson-nav {
  display: flex;
  justify-content: space-between;
  margin-top: 24px;
  padding-top: 16px;
  border-top: 1px solid var(--rule);
}

.coach-panel {
  background: var(--card);
  border-left: 1px solid var(--rule);
  padding: 16px 14px;
  display: flex;
  flex-direction: column;
  min-height: 0;
  overflow: hidden;
}

.coach-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  margin-bottom: 6px;
}

.coach-title {
  font-size: 15px;
  font-weight: 700;
  color: var(--navy);
}

.coach-tag {
  font-size: 10px;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
  border: 1px solid var(--rule);
  padding: 2px 6px;
  border-radius: 3px;
}

.coach-intro {
  margin: 0 0 10px;
  font-size: 12px;
  color: var(--muted);
  line-height: 1.45;
}

.coach-concepts {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-bottom: 10px;
}

.coach-chip {
  font-size: 11px;
  padding: 5px 8px;
  border-radius: 999px;
  border: 1px solid var(--rule);
  background: var(--paper);
  color: var(--navy);
  font-weight: 600;
  cursor: pointer;
}

.coach-chip:hover { border-color: var(--gold); }

.coach-messages {
  flex: 1;
  overflow-y: auto;
  min-height: 120px;
  max-height: 420px;
  padding: 4px 0;
  margin-bottom: 10px;
}

.coach-msg {
  font-size: 13px;
  line-height: 1.45;
  padding: 10px 11px;
  margin-bottom: 8px;
  border-radius: 6px;
  background: var(--paper);
  border: 1px solid var(--rule);
}

.coach-msg.coach strong { color: var(--navy); }

.coach-msg p { margin: 6px 0 0; }
.coach-msg ul { margin: 8px 0 0; padding-left: 18px; }
.coach-msg li { margin-bottom: 4px; }

.coach-actions {
  display: flex;
  flex-direction: column;
  gap: 8px;
  padding-top: 8px;
  border-top: 1px solid var(--rule);
}

.coach-btn { width: 100%; font-size: 13px; padding: 8px 12px; }

.mcq-panel { max-width: 720px; }

.mcq-lead { color: var(--muted); font-size: 15px; margin: 0 0 16px; }

.mcq-options { margin-bottom: 16px; }

.mcq-field {
  display: flex;
  flex-direction: column;
  gap: 6px;
  font-size: 13px;
  font-weight: 600;
  color: var(--navy);
}

.mcq-field input[type="number"] {
  font: inherit;
  padding: 8px 10px;
  border: 1px solid var(--rule);
  border-radius: 4px;
  max-width: 120px;
}

.mcq-hint { font-size: 13px; color: var(--muted); margin: 10px 0 0; }

.mcq-units {
  border: 1px solid var(--rule);
  padding: 12px 14px 10px;
  margin: 0 0 18px;
  background: var(--card);
}

.mcq-units legend {
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--muted);
  padding: 0 6px;
}

.mcq-check {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  margin: 4px 14px 4px 0;
  font-size: 14px;
  cursor: pointer;
}

.mcq-q { font-size: 20px; line-height: 1.35; margin: 0 0 8px; color: var(--navy); }

.mcq-unit-tag { font-size: 12px; color: var(--muted); margin: 0 0 16px; }

.mcq-choices {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin-bottom: 20px;
}

.mcq-choice {
  text-align: left;
  font: inherit;
  font-size: 15px;
  padding: 12px 14px;
  border: 2px solid var(--rule);
  border-radius: 6px;
  background: var(--card);
  cursor: pointer;
  color: var(--ink);
}

.mcq-choice:hover { border-color: var(--navy); }

.mcq-choice.selected {
  border-color: var(--gold);
  background: var(--paper);
  font-weight: 600;
}

.mcq-nav { flex-wrap: wrap; }

.mcq-review { margin-top: 16px; }

.mcq-review-item {
  border: 1px solid var(--rule);
  border-left: 4px solid var(--bad);
  padding: 12px 14px;
  margin-bottom: 10px;
  background: var(--card);
  font-size: 14px;
}

.mcq-wrong { color: var(--bad); }
.mcq-right { color: var(--ok); font-weight: 600; }
.mcq-explain { margin: 8px 0 0; color: var(--muted); font-size: 13px; }