:root {
  --bg: #faf9f6;
  --surface: #ffffff;
  --border: #ede9e0;
  --border2: #ddd8cc;
  --text: #1c1a16;
  --body: #4a4640;
  --muted: #8a8278;
  --dim: #c8c2b8;
  --ink: #0f0e0b;
  --accent: #2d6a4f;
  --accent-dim: rgba(45,106,79,0.08);
  --accent-border: rgba(45,106,79,0.2);
  --accent-light: #f0f7f4;
  --warm: #c45c1a;
  --warm-dim: rgba(196,92,26,0.08);
  --warm-border: rgba(196,92,26,0.2);
  --blue: #1a5fa8;
  --blue-dim: rgba(26,95,168,0.07);
  --blue-border: rgba(26,95,168,0.18);
  --red: #b83232;
  --red-dim: rgba(184,50,50,0.07);
  --red-border: rgba(184,50,50,0.18);
}
*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
html{scroll-behavior:smooth}
body{font-family:'Inter',sans-serif;background:var(--bg);color:var(--text);line-height:1.65}

/* ── HEADER ──────────────────────────────────── */
header {
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  padding: 0 40px;
  height: 60px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: 0 1px 0 var(--border);
  gap: 16px;
}
.logo { display: flex; align-items: center; gap: 12px; flex-shrink: 0; }
.logo-mark {
  width: 32px; height: 32px;
  background: var(--accent);
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  color: #fff;
  font-family: 'Fraunces', serif;
  font-size: 17px; font-weight: 500; font-style: italic;
  flex-shrink: 0;
}
.logo-text { font-size: 14px; font-weight: 500; color: var(--text); white-space: nowrap; }
.logo-text span { color: var(--accent); }
.hdr-right {
  display: flex;
  align-items: center;
  gap: 16px;
  flex-shrink: 0;
  min-width: 0;
}
.prog-wrap { display: flex; align-items: center; gap: 10px; }
.prog-track { width: 120px; height: 5px; background: var(--border); border-radius: 3px; overflow: hidden; }
.prog-fill { height: 100%; background: linear-gradient(90deg, var(--accent), #52b788); border-radius: 3px; transition: width .5s ease; width: 0%; }
.prog-pct { font-size: 12px; color: var(--accent); font-weight: 600; min-width: 32px; }
.badge {
  font-size: 11px; font-weight: 600;
  padding: 3px 10px;
  border-radius: 20px;
  background: var(--accent-dim);
  color: var(--accent);
  border: 1px solid var(--accent-border);
  white-space: nowrap;
}

/* ── LAYOUT ──────────────────────────────────── */
.shell { display: flex; min-height: calc(100svh - 60px); }

/* ── SIDEBAR ─────────────────────────────────── */
.sidebar {
  width: 248px;
  flex-shrink: 0;
  border-right: 1px solid var(--border);
  background: var(--surface);
  padding: 22px 0;
  position: sticky;
  top: 60px;
  height: calc(100svh - 60px);
  overflow-y: auto;
}
.sb-section {
  font-size: 9px; font-weight: 700;
  letter-spacing: .13em; text-transform: uppercase;
  color: var(--dim);
  padding: 0 18px;
  margin: 20px 0 6px;
}
.sb-section:first-child { margin-top: 0; }
.nav-btn {
  display: flex; align-items: center; gap: 9px;
  padding: 9px 18px;
  width: 100%; border: none; background: none;
  cursor: pointer;
  font-family: 'Inter', sans-serif;
  font-size: 13px; font-weight: 500;
  color: var(--muted);
  text-align: left;
  transition: all .12s;
  line-height: 1.3;
}
.nav-btn:hover { color: var(--text); background: var(--accent-dim); }
.nav-btn.active { color: var(--accent); background: var(--accent-dim); border-right: 3px solid var(--accent); font-weight: 600; }
.nav-btn.done { color: var(--accent); }
.nav-btn.done::after { content: '✓'; margin-left: auto; font-size: 11px; color: var(--accent); }
.nav-num {
  width: 22px; height: 22px;
  border-radius: 50%;
  font-size: 11px; font-weight: 700;
  background: var(--border); color: var(--muted);
  display: flex; align-items: center; justify-content: center;
  flex-shrink: 0;
}
.nav-btn.active .nav-num { background: var(--accent); color: #fff; }
.nav-btn.done .nav-num { background: var(--accent-dim); color: var(--accent); border: 1px solid var(--accent-border); }

/* ── MAIN ────────────────────────────────────── */
.main { flex: 1; min-width: 0; padding: 52px 64px 88px; }

/* ── LESSON ──────────────────────────────────── */
.lesson { display: none; }
.lesson.active { display: block; animation: fadeUp .28s ease; }
@keyframes fadeUp { from { opacity: 0; transform: translateY(8px); } to { opacity: 1; transform: translateY(0); } }
.lesson-eyebrow { display: flex; align-items: center; gap: 10px; margin-bottom: 14px; }
.ey-num { font-size: 11px; font-weight: 700; color: var(--accent); letter-spacing: .06em; }
.ey-dot { width: 3px; height: 3px; background: var(--dim); border-radius: 50%; }
.ey-cat { font-size: 11px; color: var(--muted); font-weight: 500; }
.lesson h2 {
  font-family: 'Fraunces', serif;
  font-size: clamp(1.6rem, 3vw, 2.7rem);
  font-weight: 300; color: var(--ink);
  line-height: 1.15;
  margin-bottom: 16px;
  letter-spacing: -.01em;
}
.lesson h2 em { color: var(--accent); font-style: italic; }
.lesson-intro {
  font-size: .97rem; color: var(--muted);
  max-width: 600px; line-height: 1.8;
  margin-bottom: 40px;
  padding-left: 16px;
  border-left: 3px solid var(--accent);
}

/* ── PROSE ───────────────────────────────────── */
.prose { max-width: 720px; }
.prose p { font-size: .94rem; color: var(--body); line-height: 1.85; margin-bottom: 18px; }
.prose h3 { font-family: 'Fraunces', serif; font-size: 1.22rem; font-weight: 500; color: var(--ink); margin: 32px 0 12px; }
.prose ul, .prose ol { padding-left: 22px; margin-bottom: 18px; }
.prose li { font-size: .92rem; color: var(--body); margin-bottom: 8px; line-height: 1.75; }
.prose strong { color: var(--ink); font-weight: 600; }
.prose code { font-family: 'JetBrains Mono', monospace; font-size: .82em; background: var(--border); color: var(--warm); padding: 1px 6px; border-radius: 3px; }

/* ── ANALOGY CARD ────────────────────────────── */
.analogy {
  background: var(--accent-light); border: 1px solid var(--accent-border);
  border-radius: 10px; padding: 22px 24px;
  margin: 22px 0; max-width: 720px;
  display: flex; gap: 16px;
}
.analogy-ico { font-size: 26px; flex-shrink: 0; line-height: 1; }
.analogy-body h4 { font-family: 'Fraunces', serif; font-size: 1rem; font-weight: 500; color: var(--accent); margin-bottom: 6px; }
.analogy-body p { font-size: .9rem; color: #2d4a3e; line-height: 1.75; margin: 0; }

/* ── PLAIN ENGLISH BLOCK ─────────────────────── */
.plain-block {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: 8px; padding: 20px 22px;
  margin: 18px 0; max-width: 720px;
  font-family: 'JetBrains Mono', monospace;
  font-size: .84rem; line-height: 2; color: var(--body);
  overflow-x: auto;
}
.plain-block .eng { color: var(--muted); font-style: italic; display: block; white-space: nowrap; }
.plain-block .code { color: var(--ink); display: block; padding-left: 20px; border-left: 2px solid var(--accent); white-space: nowrap; }
.plain-block .arrow { color: var(--accent); font-weight: 700; }

/* ── CALLOUT ─────────────────────────────────── */
.callout {
  display: flex; gap: 14px;
  padding: 16px 18px; border-radius: 8px;
  margin: 20px 0;
  font-size: .91rem; line-height: 1.75;
  max-width: 720px;
}
.callout-ico { font-size: 18px; flex-shrink: 0; margin-top: 1px; }
.callout-body { flex: 1; }
.callout-body strong { display: block; font-size: .89rem; margin-bottom: 4px; font-weight: 600; }
.callout-body p { color: var(--body); margin: 0; font-size: .87rem; }
.callout.tip { background: var(--blue-dim); border: 1px solid var(--blue-border); }
.callout.tip strong { color: var(--blue); }
.callout.warn { background: var(--warm-dim); border: 1px solid var(--warm-border); }
.callout.warn strong { color: var(--warm); }
.callout.good { background: var(--accent-dim); border: 1px solid var(--accent-border); }
.callout.good strong { color: var(--accent); }

/* ── CONCEPT TABLE ───────────────────────────── */
.concept-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin: 18px 0;
  max-width: 720px;
}
.concept-cell { background: var(--surface); border: 1px solid var(--border); border-radius: 8px; padding: 16px; }
.concept-cell-label {
  font-size: 10px; font-weight: 700;
  letter-spacing: .1em; text-transform: uppercase;
  margin-bottom: 6px;
}
/* color modifiers — replaces inline style="color:var(...)" */
.ccl--accent { color: var(--accent); }
.ccl--warm   { color: var(--warm); }
.ccl--blue   { color: var(--blue); }
.ccl--muted  { color: var(--muted); }

.concept-cell h4 { font-size: .93rem; font-weight: 600; color: var(--ink); margin-bottom: 5px; }
.concept-cell p { font-size: .83rem; color: var(--muted); line-height: 1.6; margin: 0; }

/* ── INTERACTIVE BOX ─────────────────────────── */
.interactive-box {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: 10px; padding: 24px;
  margin: 22px 0; max-width: 720px;
}
.ib-label { font-size: 10px; font-weight: 700; letter-spacing: .1em; text-transform: uppercase; color: var(--accent); margin-bottom: 16px; }
.ib-desc { font-size: .89rem; color: var(--body); margin-bottom: 14px; }

/* shared interactive controls */
.ib-controls { display: flex; flex-direction: column; gap: 14px; }
.ib-row { display: flex; align-items: center; gap: 12px; }
.ib-row--mb { margin-bottom: 16px; }
.ib-lbl { font-size: 13px; color: var(--muted); min-width: 60px; }
.ib-range { flex: 1; }
.ib-val { font-size: 13px; font-weight: 600; color: var(--ink); min-width: 50px; text-align: right; white-space: nowrap; }
.ib-select {
  flex: 1;
  font-family: inherit; font-size: 13px;
  padding: 6px 10px;
  border: 1px solid var(--border2);
  border-radius: 6px;
  background: var(--bg); color: var(--text);
}
.ticket-result {
  background: var(--accent-light);
  border: 1px solid var(--accent-border);
  border-radius: 7px;
  padding: 14px 16px;
  font-size: .9rem; color: var(--accent); font-weight: 600;
  font-family: 'JetBrains Mono', monospace;
  overflow-x: auto;
  word-break: break-word;
}

/* loop visualiser */
.loop-viz { display: flex; gap: 8px; flex-wrap: wrap; margin-bottom: 14px; }
.loop-box {
  width: 44px; height: 44px;
  border-radius: 7px;
  border: 1px solid var(--border);
  background: var(--surface);
  display: flex; align-items: center; justify-content: center;
  font-family: 'JetBrains Mono', monospace;
  font-size: .82rem; color: var(--dim);
  transition: background .2s, color .2s, border-color .2s;
}
.loop-box--done { background: var(--accent); color: #fff; border-color: var(--accent); }
.loop-msg { margin-top: 12px; font-size: .87rem; color: var(--muted); font-family: 'JetBrains Mono', monospace; }

/* interactive buttons */
.ib-btn-row { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; }
.ib-btn-row--gap { margin-top: 14px; }
.ib-btn {
  font-family: 'Inter', sans-serif;
  font-size: 12px; font-weight: 600;
  padding: 8px 16px;
  border-radius: 6px; cursor: pointer;
  border: none; transition: opacity .15s;
}
.ib-btn:disabled { opacity: .4; cursor: not-allowed; }
.ib-btn--accent { background: var(--accent); color: #fff; }
.ib-btn--ghost { background: var(--surface); color: var(--muted); border: 1px solid var(--border2); }

/* trace execution */
.trace-steps { display: flex; flex-direction: column; gap: 4px; font-family: 'JetBrains Mono', monospace; font-size: .84rem; }
.trace-step {
  display: flex; gap: 10px;
  padding: 8px 10px;
  border-radius: 5px;
  opacity: .35;
  transition: all .25s;
  border-left: 3px solid transparent;
}
.trace-step--active { opacity: 1; background: var(--accent-dim); border-left-color: var(--accent); }
.trace-num { color: var(--dim); min-width: 20px; font-size: .82rem; }
.trace-line { color: var(--ink); }
.mem-box { font-size: .82rem; color: var(--muted); font-family: 'JetBrains Mono', monospace; margin-left: 8px; }

/* ── TYPE QUIZ ───────────────────────────────── */
.tq-list { display: flex; flex-direction: column; gap: 10px; }
.tq-item {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 7px;
  padding: 14px 16px;
}
.tq-label { font-size: .88rem; font-weight: 600; color: var(--ink); margin-bottom: 10px; }
.tq-opts { display: flex; gap: 8px; flex-wrap: wrap; }
.tq-btn {
  font-family: 'Inter', sans-serif;
  font-size: 12px; padding: 5px 12px;
  border: 1px solid var(--border2);
  border-radius: 5px;
  background: var(--surface);
  color: var(--muted);
  cursor: pointer;
  transition: background .12s, color .12s, border-color .12s;
}
.tq-btn:hover:not(:disabled) { border-color: var(--accent); color: var(--text); background: var(--accent-light); }
.tq-btn:disabled { cursor: default; }
.tq-btn--correct { background: var(--accent-dim) !important; border-color: var(--accent-border) !important; color: var(--accent) !important; }
.tq-btn--wrong   { background: var(--red-dim) !important; border-color: var(--red-border) !important; color: var(--red) !important; }
.tq-fb { font-size: .82rem; margin-top: 8px; display: none; }
.tq-fb--show { display: block; }
.tq-fb--ok  { color: var(--accent); }
.tq-fb--bad { color: var(--red); }

/* ── QUIZ ────────────────────────────────────── */
.quiz { background: var(--surface); border: 1px solid var(--border); border-radius: 10px; padding: 24px; margin: 32px 0; max-width: 720px; }
.quiz-label { font-size: 10px; font-weight: 700; letter-spacing: .12em; text-transform: uppercase; color: var(--accent); margin-bottom: 12px; }
.quiz-q { font-size: .95rem; font-weight: 600; color: var(--ink); margin-bottom: 18px; line-height: 1.55; }
.quiz-opts { display: flex; flex-direction: column; gap: 9px; }
.quiz-opt {
  background: var(--bg); border: 1px solid var(--border2);
  border-radius: 6px; padding: 11px 15px;
  cursor: pointer;
  font-family: 'Inter', sans-serif; font-size: .89rem; font-weight: 500;
  color: var(--muted); text-align: left;
  transition: all .12s;
}
.quiz-opt:hover:not(:disabled) { border-color: var(--accent); color: var(--text); background: var(--accent-light); }
.quiz-opt.correct { border-color: var(--accent); color: var(--accent); background: var(--accent-dim); }
.quiz-opt.wrong   { border-color: var(--red); color: var(--red); background: var(--red-dim); }
.quiz-opt:disabled { cursor: default; }
.quiz-fb { margin-top: 14px; padding: 11px 15px; border-radius: 6px; font-size: .87rem; font-weight: 600; display: none; }
.quiz-fb.show { display: block; }
.quiz-fb.ok  { background: var(--accent-dim); color: var(--accent); border: 1px solid var(--accent-border); }
.quiz-fb.bad { background: var(--red-dim);    color: var(--red);    border: 1px solid var(--red-border); }

/* ── LESSON NAV ──────────────────────────────── */
.lesson-nav {
  display: flex; justify-content: space-between; align-items: center;
  margin-top: 56px; padding-top: 24px;
  border-top: 1px solid var(--border);
  max-width: 720px;
  gap: 12px;
}
.btn { font-family: 'Inter', sans-serif; font-size: 13px; font-weight: 600; padding: 11px 22px; border-radius: 7px; cursor: pointer; border: none; transition: all .15s; }
.btn-next { background: var(--accent); color: #fff; }
.btn-next:hover:not(:disabled) { background: #1f4f3a; transform: translateY(-1px); }
.btn-prev { background: var(--surface); color: var(--muted); border: 1px solid var(--border2); }
.btn-prev:hover { color: var(--text); border-color: var(--accent); }
.btn:disabled { opacity: .3; cursor: not-allowed; transform: none !important; }

/* ── BRIDGE BLOCK ────────────────────────────── */
.bridge {
  background: #0f0e0b; border-radius: 10px;
  padding: 22px 24px; margin: 20px 0; max-width: 720px;
  font-family: 'JetBrains Mono', monospace;
  font-size: .84rem; line-height: 2;
  overflow-x: auto;
}
.br-label { font-size: 9px; font-weight: 700; letter-spacing: .14em; text-transform: uppercase; color: #5a6a5a; margin-bottom: 12px; }
.br-eng  { color: #4a5a4a; display: block; white-space: nowrap; }
.br-java { color: #e2e8e2; display: block; padding-left: 20px; border-left: 2px solid #2d6a4f; white-space: nowrap; }
.br-kw   { color: #c084fc; }
.br-cl   { color: #fbbf24; }
.br-fn   { color: #4ade80; }
.br-str  { color: #fb923c; }
.br-cm   { color: #3d4d3d; font-style: italic; }
.br-num  { color: #f472b6; }

/* ── BACK LINK ───────────────────────────────── */
.back-link {
  position: fixed;
  bottom: 24px; left: 24px;
  z-index: 999;
  display: flex; align-items: center; gap: 8px;
  background: #161b22; color: #e6edf3;
  text-decoration: none;
  padding: 10px 18px;
  border-radius: 50px;
  font-family: sans-serif; font-size: 13px; font-weight: 600;
  border: 1px solid #30363d;
  box-shadow: 0 8px 16px rgba(0,0,0,0.4);
  transition: background .2s, transform .2s;
}
.back-link:hover { background: #21262d; transform: translateY(-2px); }

/* ── MOBILE LESSON NAV ───────────────────────── */
.mobile-nav { display: none; margin-bottom: 24px; }
.mobile-lesson-select {
  width: 100%;
  font-family: 'Inter', sans-serif;
  font-size: 13px; font-weight: 500;
  padding: 10px 14px;
  border: 1px solid var(--border2);
  border-radius: 8px;
  background: var(--surface);
  color: var(--text);
  cursor: pointer;
}

/* ── SCROLLBAR ───────────────────────────────── */
::-webkit-scrollbar { width: 4px; }
::-webkit-scrollbar-thumb { background: var(--border2); border-radius: 2px; }

/* ── RESPONSIVE ──────────────────────────────── */

/* Tablet — hide sidebar, give main room */
@media (max-width: 860px) {
  header { padding: 0 20px; }
  .badge { display: none; }
  .sidebar { display: none; }
  .mobile-nav { display: block; }
  .main { padding: 32px 28px 72px; }
}

/* Phablet */
@media (max-width: 600px) {
  header { padding: 0 14px; height: auto; min-height: 56px; flex-wrap: wrap; padding-top: 10px; padding-bottom: 10px; }
  .prog-track { width: 80px; }
  .main { padding: 24px 16px 64px; }
  .lesson-intro { font-size: .92rem; margin-bottom: 28px; }
  .concept-row { grid-template-columns: 1fr; }
  .analogy { flex-direction: column; gap: 10px; }
  .analogy-ico { font-size: 20px; }
  .callout { flex-direction: column; gap: 8px; }
  .ib-controls { gap: 12px; }
  .ib-row { flex-wrap: wrap; }
  .ib-lbl { min-width: auto; }
  .ib-range { min-width: 120px; }
  .lesson-nav { flex-direction: column-reverse; align-items: stretch; }
  .lesson-nav .btn { text-align: center; }
  .back-link { bottom: 16px; left: 12px; padding: 8px 14px; font-size: 12px; }
  .mem-box { margin-left: 0; display: block; width: 100%; margin-top: 8px; }
  .ib-btn-row { flex-wrap: wrap; }
}

/* Small mobile */
@media (max-width: 400px) {
  .logo-text { display: none; }
  .prog-track { width: 60px; }
  .main { padding: 20px 12px 60px; }
  .bridge { padding: 16px 14px; }
  .interactive-box { padding: 16px; }
  .quiz { padding: 16px; }
  .loop-box { width: 36px; height: 36px; font-size: .75rem; }
  .tq-opts { gap: 6px; }
  .tq-btn { font-size: 11px; padding: 4px 9px; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: 0.01ms !important; transition-duration: 0.01ms !important; }
}
/* Mobile Responsive Overrides */
@media (max-width: 768px) {
    .shell, .layout { 
        flex-direction: column !important; 
    }
    .sidebar { 
        width: 100% !important; 
        position: static !important;
        margin-bottom: 20px;
    }
    .main { 
        width: 100% !important; 
        padding: 15px !important;
    }
    .lesson-nav { 
        flex-direction: column; 
        gap: 10px; 
    }
    button, .nav-btn, .btn { 
        min-height: 44px !important; 
        padding: 12px !important;
    }
}