*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg: #111317;
  --surface: #1a1d23;
  --border: #2a2d35;
  --accent: #00d4aa;
  --accent2: #5794f2;
  --text: #d4d9e0;
  --text-muted: #6b7280;
  --topbar-h: 52px;
}

body { background: var(--bg); color: var(--text); font-family: 'Segoe UI', system-ui, sans-serif; height: 100vh; overflow: hidden; }

/* ── Topbar ── */
.topbar {
  height: var(--topbar-h); background: var(--surface); border-bottom: 1px solid var(--border);
  display: flex; align-items: center; justify-content: space-between; padding: 0 16px; gap: 12px;
}
.topbar-left, .topbar-right { display: flex; align-items: center; gap: 10px; }
.logo { font-weight: 700; font-size: 1rem; color: var(--accent); white-space: nowrap; }

.exercise-select {
  background: var(--bg); color: var(--text); border: 1px solid var(--border);
  padding: 5px 10px; border-radius: 6px; font-size: 0.875rem; cursor: pointer; min-width: 200px;
}
.exercise-select:focus { outline: none; border-color: var(--accent); }
.step-counter { font-size: 0.8rem; color: var(--text-muted); white-space: nowrap; }
.btn {
  background: var(--surface); color: var(--text); border: 1px solid var(--border);
  padding: 5px 14px; border-radius: 6px; cursor: pointer; font-size: 0.85rem; transition: all .15s;
}
.btn:hover:not(:disabled) { border-color: var(--accent); color: var(--accent); }
.btn:disabled { opacity: 0.35; cursor: not-allowed; }
.btn-icon { padding: 5px 11px; font-size: 1.05rem; }

/* ── Split layout ── */
.split {
  display: grid;
  grid-template-columns: 65% 1fr;
  height: calc(100vh - var(--topbar-h));
  overflow: hidden;
}
.split.panel-hidden { /* managed by JS */ }
.split.panel-hidden .pane-right,
.split.panel-hidden .resize-handle { display: none; }

/* ── Panes ── */
.pane-left { background: #000; overflow: hidden; }
.pane-left iframe { width: 100%; height: 100%; border: none; display: block; }
.pane-right { display: flex; flex-direction: column; overflow: hidden; min-width: 0; }

.tutorial-title {
  padding: 11px 16px 9px; font-size: 0.81rem; font-weight: 600; color: var(--accent2);
  border-bottom: 1px solid var(--border); background: var(--surface);
  white-space: nowrap; overflow: hidden; text-overflow: ellipsis; flex-shrink: 0;
}
.tutorial-content {
  flex: 1; overflow-y: auto; overflow-x: hidden;
  padding: 16px 18px; font-size: 0.88rem; line-height: 1.65;
}
.placeholder { color: var(--text-muted); margin-top: 40px; text-align: center; }

/* ── Markdown: headings ── */
.tutorial-content h1 { font-size: 1.2rem; color: var(--accent); margin: 0 0 10px; padding-bottom: 6px; border-bottom: 1px solid var(--border); }
.tutorial-content h2 { font-size: 0.97rem; color: var(--accent2); margin: 18px 0 8px; padding: 6px 10px; border-left: 3px solid var(--accent2); background: rgba(87,148,242,.07); border-radius: 0 4px 4px 0; }
.tutorial-content h3 { font-size: 0.91rem; color: var(--text); margin: 14px 0 5px; }
.tutorial-content h4 { font-size: 0.87rem; color: var(--text-muted); margin: 10px 0 4px; }
.tutorial-content p { margin-bottom: 10px; }
.tutorial-content hr { border: none; border-top: 1px solid var(--border); margin: 14px 0; }

/* ── Lists with checkboxes ── */
.tutorial-content ul, .tutorial-content ol { padding-left: 0; margin: 0 0 10px 0; list-style: none; }
.tutorial-content li { display: flex; align-items: flex-start; gap: 7px; padding: 3px 0; }
.tutorial-content li.checked { opacity: 0.6; }
.tutorial-content li.checked .li-text { text-decoration: line-through; color: var(--text-muted); }
.li-num  { color: var(--accent2); font-weight: 700; font-size: 0.82em; min-width: 18px; flex-shrink: 0; margin-top: 2px; text-align: right; }
.li-bullet { color: var(--accent2); flex-shrink: 0; line-height: 1.65; }
.li-text { flex: 1; min-width: 0; }

/* ── Checkbox ── */
.task-check {
  appearance: none; -webkit-appearance: none;
  width: 15px; height: 15px; min-width: 15px;
  border: 1.5px solid var(--border); border-radius: 3px;
  cursor: pointer; margin-top: 3px; flex-shrink: 0;
  background: transparent; transition: all 0.15s; position: relative;
}
.task-check:hover { border-color: var(--accent); }
.task-check:checked { background: var(--accent); border-color: var(--accent); }
.task-check:checked::after {
  content: ''; position: absolute;
  left: 4px; top: 1px; width: 4px; height: 8px;
  border: 2px solid #071410; border-top: none; border-left: none;
  transform: rotate(45deg);
}

/* ── Inline code — copyable ── */
.tutorial-content code {
  background: var(--surface); border: 1px solid var(--border);
  padding: 1px 6px; border-radius: 4px;
  font-family: 'Consolas', 'Cascadia Code', monospace; font-size: 0.82em; color: #e06c75;
}
.tutorial-content code.copyable { cursor: pointer; transition: background 0.12s, color 0.12s; user-select: none; }
.tutorial-content code.copyable::after { content: ' 📋'; font-size: 0.72em; opacity: 0; transition: opacity 0.1s; }
.tutorial-content code.copyable:hover::after { opacity: 0.6; }
.tutorial-content code.copyable:hover { background: #2a1520; border-color: #c05060; }
.tutorial-content code.copyable.copied { background: var(--accent) !important; color: #071410 !important; border-color: var(--accent) !important; }
.tutorial-content code.copyable.copied::after { content: ' ✓'; opacity: 1 !important; }

/* ── Code blocks ── */
.tutorial-content pre { background: #0d1117; border: 1px solid var(--border); border-radius: 6px; padding: 12px; overflow-x: auto; margin-bottom: 12px; }
.tutorial-content pre code { background: none; border: none; padding: 0; color: inherit; font-size: 0.82rem; cursor: default; }
.tutorial-content pre code::after { display: none; }

/* ── Tables ── */
.tutorial-content table { border-collapse: collapse; width: 100%; margin-bottom: 12px; font-size: 0.83rem; }
.tutorial-content th { background: var(--surface); padding: 6px 10px; text-align: left; border: 1px solid var(--border); color: var(--accent2); }
.tutorial-content td { padding: 5px 10px; border: 1px solid var(--border); }
.tutorial-content strong { color: #f0f0f0; }

/* ── Callouts ── */
.callout { border-radius: 6px; padding: 10px 14px; margin-bottom: 12px; font-size: 0.85rem; }
.callout-note { background: #1a2744; border-left: 3px solid var(--accent2); }
.callout-tip  { background: #1a2f2a; border-left: 3px solid var(--accent); }
.callout-warn { background: #2f2010; border-left: 3px solid #e5a000; }
.callout-label { font-weight: 700; margin-bottom: 4px; font-size: 0.8rem; text-transform: uppercase; letter-spacing: .05em; }
.callout-note .callout-label { color: var(--accent2); }
.callout-tip  .callout-label { color: var(--accent); }
.callout-warn .callout-label { color: #e5a000; }
.tutorial-content blockquote { border-left: 3px solid var(--text-muted); margin: 8px 0; padding: 6px 12px; background: var(--surface); border-radius: 0 4px 4px 0; color: var(--text-muted); }

/* ── Scrollbar ── */
::-webkit-scrollbar { width: 5px; height: 5px; }
::-webkit-scrollbar-track { background: var(--bg); }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: #3a3d45; }

/* ── Collapsible Task Sections ── */
.task-section { margin-bottom: 6px; }
.task-body { overflow: hidden; transition: max-height 0.35s ease; }
.task-heading { cursor: pointer; user-select: none; display: flex; align-items: center; gap: 6px; }
.task-heading:hover { opacity: 0.85; }
.task-icon { font-size: 0.75em; flex-shrink: 0; transition: transform 0.2s; }
.task-heading.task-complete { color: var(--accent) !important; border-left-color: var(--accent) !important; background: rgba(0,212,170,.12) !important; }
.course-title { color: var(--text-muted); font-size: 0.85rem; margin-left: 4px; }