:root {
  --bg: #f7f6f2;
  --surface: #ffffff;
  --card: #fefefe;
  --border: #e8e4da;
  --border2: #d4cfc3;
  --text: #1a1814;
  --body: #3d3830;
  --muted: #8a8070;
  --dim: #b8b0a0;
  --ink: #2c2820;
  --java: #e65c00;
  --java-dim: rgba(230,92,0,0.08);
  --java-border: rgba(230,92,0,0.2);
  --java-light: #fff4ed;
  --green: #2d7a47;
  --green-dim: rgba(45,122,71,0.08);
  --green-border: rgba(45,122,71,0.2);
  --blue: #1a5fad;
  --blue-dim: rgba(26,95,173,0.07);
  --blue-border: rgba(26,95,173,0.18);
  --red: #c0392b;
  --red-dim: rgba(192,57,43,0.07);
  --red-border: rgba(192,57,43,0.18);
  --purple: #6c3a9e;
  --purple-dim: rgba(108,58,158,0.07);
}
*, *::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: 1.6; }

/* 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 4px rgba(0,0,0,0.05);
}
.logo { display: flex; align-items: center; gap: 10px; text-decoration: none; }
.logo-icon {
  width: 32px; height: 32px; background: var(--java); border-radius: 8px;
  display: flex; align-items: center; justify-content: center;
  font-family: 'JetBrains Mono', monospace; font-size: 13px; font-weight: 500; color: #fff;
}
.logo-text { font-size: 15px; font-weight: 700; color: var(--text); }
.logo-text span { color: var(--java); }
.header-meta { display: flex; align-items: center; gap: 20px; }
.prog-wrap { display: flex; align-items: center; gap: 10px; }
.prog-label { font-size: 12px; color: var(--muted); font-weight: 600; }
.prog-track { width: 140px; height: 6px; background: var(--border); border-radius: 3px; overflow: hidden; }
.prog-fill { height: 100%; background: linear-gradient(90deg, var(--java), #f59e0b); border-radius: 3px; transition: width .5s ease; width: 0%; }
.prog-pct { font-size: 12px; color: var(--java); font-weight: 700; min-width: 34px; }
.badge { font-size: 11px; font-weight: 600; padding: 3px 10px; border-radius: 20px; background: var(--java-dim); color: var(--java); border: 1px solid var(--java-border); }

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

/* SIDEBAR */
.sidebar {
  width: 268px; flex-shrink: 0; border-right: 1px solid var(--border);
  background: var(--surface); padding: 24px 0;
  position: sticky; top: 60px; height: calc(100vh - 60px); overflow-y: auto;
}
.sb-section { font-size: 10px; font-weight: 700; letter-spacing: .1em; text-transform: uppercase; color: var(--dim); padding: 0 20px; margin: 20px 0 6px; }
.sb-section:first-child { margin-top: 0; }
.nav-btn {
  display: flex; align-items: center; gap: 10px; padding: 8px 20px;
  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;
}
.nav-btn:hover { color: var(--text); background: var(--java-dim); }
.nav-btn.active { color: var(--java); background: var(--java-dim); border-right: 3px solid var(--java); font-weight: 600; }
.nav-btn.done { color: var(--green); }
.nav-btn.done::after { content: '✓'; margin-left: auto; font-size: 12px; color: var(--green); }
.nav-num {
  width: 22px; height: 22px; border-radius: 6px; 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(--java); color: #fff; }
.nav-btn.done .nav-num { background: var(--green-dim); color: var(--green); border: 1px solid var(--green-border); }

/* MAIN */
.main { flex: 1; min-width: 0; padding: 52px 64px 80px; }

/* LESSON */
.lesson { display: none; }
.lesson.active { display: block; animation: fadeUp .28s ease; }
@keyframes fadeUp { from { opacity:0; transform: translateY(10px); } to { opacity:1; transform:translateY(0); } }

.lesson-eyebrow { display: flex; align-items: center; gap: 10px; margin-bottom: 12px; }
.eyebrow-num { font-size: 12px; font-weight: 700; color: var(--java); letter-spacing: .06em; }
.eyebrow-dot { width: 4px; height: 4px; background: var(--dim); border-radius: 50%; }
.eyebrow-cat { font-size: 12px; color: var(--muted); font-weight: 500; }

.lesson h2 {
  font-family: 'Lora', serif; font-size: clamp(1.8rem, 3vw, 2.6rem);
  font-weight: 600; color: var(--ink); line-height: 1.2; margin-bottom: 14px;
}
.lesson-intro {
  font-size: 1rem; color: var(--muted); max-width: 620px; line-height: 1.75;
  margin-bottom: 36px; padding-left: 14px; border-left: 3px solid var(--java);
}

/* PROSE */
.prose { max-width: 760px; }
.prose p { font-size: .95rem; color: var(--body); line-height: 1.8; margin-bottom: 16px; }
.prose h3 { font-family: 'Lora', serif; font-size: 1.25rem; font-weight: 600; color: var(--ink); margin: 32px 0 12px; }
.prose ul, .prose ol { padding-left: 20px; margin-bottom: 16px; }
.prose li { font-size: .93rem; color: var(--body); margin-bottom: 7px; line-height: 1.7; }
.prose strong { color: var(--ink); font-weight: 600; }
.prose code { font-family: 'JetBrains Mono', monospace; font-size: .82em; background: var(--border); color: var(--java); padding: 1px 6px; border-radius: 4px; }
.prose a { color: var(--java); text-decoration: underline; }

/* CODE BLOCK */
.code-wrap { margin: 20px 0; border-radius: 10px; overflow: hidden; border: 1px solid var(--border2); }
.code-top { background: #1e1c18; display: flex; align-items: center; justify-content: space-between; padding: 10px 18px; }
.code-fname { font-family: 'JetBrains Mono', monospace; font-size: 12px; color: #a0998a; display: flex; align-items: center; gap: 8px; }
.code-fname::before { content:''; width:10px; height:10px; background:var(--java); border-radius:50%; flex-shrink:0; }
.code-tag { font-size: 11px; color: #6a6258; letter-spacing: .04em; font-family: 'JetBrains Mono', monospace; }
pre {
  background: #ffffff; padding: 22px 22px; overflow-x: auto;
  font-family: 'JetBrains Mono', monospace; font-size: .84rem; line-height: 2;
  margin: 0;
}
/* syntax */
.kw   { color: #e06c75; }
.cl   { color: #e5c07b; }
.fn   { color: #61afef; }
.str  { color: #98c379; }
.num  { color: #d19a66; }
.cm   { color: #5c6370; font-style: italic; }
.ann  { color: #c678dd; }
.op   { color: #abb2bf; }
.bool { color: #56b6c2; }

/* CALLOUT */
.callout {
  display: flex; gap: 14px; padding: 16px 18px; border-radius: 8px;
  margin: 20px 0; font-size: .92rem; line-height: 1.75; max-width: 760px;
}
.callout-ico { font-size: 18px; flex-shrink: 0; margin-top: 1px; }
.callout-body { flex: 1; }
.callout-body strong { display: block; font-size: .9rem; margin-bottom: 4px; }
.callout-body p { color: #5a5040; margin: 0; font-size: .88rem; }
.callout.tip   { background: var(--blue-dim);   border: 1px solid var(--blue-border); }
.callout.tip   strong { color: var(--blue); }
.callout.warn  { background: var(--java-dim);   border: 1px solid var(--java-border); }
.callout.warn  strong { color: var(--java); }
.callout.good  { background: var(--green-dim);  border: 1px solid var(--green-border); }
.callout.good  strong { color: var(--green); }
.callout.error { background: var(--red-dim);    border: 1px solid var(--red-border); }
.callout.error strong { color: var(--red); }

/* CONCEPT GRID */
.grid-2 { display: grid; grid-template-columns: repeat(auto-fit, minmax(220px,1fr)); gap: 14px; margin: 20px 0; max-width: 760px; }
.concept-card { background: var(--surface); border: 1px solid var(--border); border-radius: 8px; padding: 18px; }
.concept-tag { font-size: 10px; font-weight: 700; letter-spacing: .1em; text-transform: uppercase; margin-bottom: 7px; }
.concept-card h4 { font-size: .93rem; font-weight: 600; margin-bottom: 5px; color: var(--ink); }
.concept-card p { font-size: .82rem; color: var(--muted); line-height: 1.6; margin: 0; }

/* TABLE */
.tbl-wrap { overflow-x: auto; margin: 18px 0; max-width: 760px; }
table { width: 100%; border-collapse: collapse; font-size: .88rem; }
th { text-align: left; padding: 9px 14px; font-size: 11px; font-weight: 700; letter-spacing: .07em; text-transform: uppercase; color: var(--muted); border-bottom: 2px solid var(--border); background: var(--bg); }
td { padding: 10px 14px; border-bottom: 1px solid var(--border); color: var(--body); vertical-align: top; }
td:first-child { font-family: 'JetBrains Mono', monospace; font-size: .82rem; color: var(--java); font-weight: 500; }
tr:last-child td { border-bottom: none; }
tr:hover td { background: var(--java-dim); }

/* QUIZ */
.quiz { background: var(--surface); border: 1px solid var(--border); border-radius: 10px; padding: 26px; margin: 32px 0; max-width: 760px; }
.quiz-eyebrow { font-size: 10px; font-weight: 700; letter-spacing: .12em; text-transform: uppercase; color: var(--java); margin-bottom: 12px; }
.quiz-q { font-size: .96rem; 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(--java); color: var(--text); background: var(--java-light); }
.quiz-opt.correct { border-color: var(--green); color: var(--green); background: var(--green-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(--green-dim); color: var(--green); border: 1px solid var(--green-border); }
.quiz-fb.bad { background: var(--red-dim);   color: var(--red);   border: 1px solid var(--red-border);   }

/* CHALLENGE */
.challenge {
  background: var(--java-light); border: 1px solid var(--java-border);
  border-radius: 10px; padding: 24px; margin: 28px 0; max-width: 760px;
  position: relative; overflow: hidden;
}
.challenge::before { content: ''; position: absolute; top:0; left:0; right:0; height: 3px; background: var(--java); }
.ch-label { font-size: 10px; font-weight: 700; letter-spacing: .1em; text-transform: uppercase; color: var(--java); margin-bottom: 10px; }
.challenge h4 { font-size: .97rem; font-weight: 700; color: var(--ink); margin-bottom: 8px; }
.challenge p { font-size: .9rem; color: var(--body); line-height: 1.7; margin-bottom: 8px; }
.challenge ul { padding-left: 16px; }
.challenge li { font-size: .88rem; color: var(--body); margin-bottom: 5px; line-height: 1.65; }
.challenge code { font-family: 'JetBrains Mono', monospace; font-size: .82em; color: var(--java); }

/* 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: 760px; }
.btn { font-family: 'Inter', sans-serif; font-size: 13px; font-weight: 600; padding: 10px 22px; border-radius: 7px; cursor: pointer; border: none; transition: all .15s; }
.btn-next { background: var(--java); color: #fff; }
.btn-next:hover:not(:disabled) { background: #cc5200; transform: translateY(-1px); box-shadow: 0 4px 12px rgba(230,92,0,.25); }
.btn-prev { background: var(--surface); color: var(--muted); border: 1px solid var(--border2); }
.btn-prev:hover { color: var(--text); border-color: var(--java); }
.btn:disabled { opacity: .35; cursor: not-allowed; transform: none !important; box-shadow: none !important; }

/* REAL WORLD BANNER */
.rw-banner { background: linear-gradient(135deg, #1a1814, #2c2420); border-radius: 10px; padding: 20px 22px; margin: 24px 0; max-width: 760px; display: flex; gap: 14px; align-items: flex-start; }
.rw-icon { font-size: 20px; flex-shrink: 0; }
.rw-text strong { display: block; color: #f5a623; font-size: .92rem; margin-bottom: 4px; }
.rw-text p { color: #a09080; font-size: .86rem; line-height: 1.65; margin: 0; }

/* STEP LIST */
.steps { counter-reset: step; display: flex; flex-direction: column; gap: 0; margin: 20px 0; max-width: 760px; }
.step { display: flex; gap: 16px; padding: 16px 0; border-bottom: 1px solid var(--border); }
.step:last-child { border-bottom: none; }
.step-num { width: 30px; height: 30px; border-radius: 50%; background: var(--java); color: #fff; font-size: 13px; font-weight: 700; display: flex; align-items: center; justify-content: center; flex-shrink: 0; margin-top: 1px; }
.step-body h4 { font-size: .93rem; font-weight: 600; color: var(--ink); margin-bottom: 4px; }
.step-body p { font-size: .87rem; color: var(--body); line-height: 1.65; margin: 0; }

/* SCROLLBAR */
::-webkit-scrollbar { width: 5px; height: 5px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border2); border-radius: 3px; }

/* ─────────────────────────────────────────────
   HAMBURGER BUTTON
   Hidden on desktop, shown on mobile
   ───────────────────────────────────────────── */
.menu-toggle {
  display: none;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  gap: 5px;
  background: none;
  border: none;
  cursor: pointer;
  padding: 6px 8px;
  border-radius: 6px;
  color: var(--text);
  transition: background .12s;
  flex-shrink: 0;
}
.menu-toggle:hover { background: var(--java-dim); }
.menu-toggle span {
  display: block;
  width: 20px;
  height: 2px;
  background: currentColor;
  border-radius: 2px;
  transition: transform .22s ease, opacity .22s ease;
  transform-origin: center;
}
.menu-toggle.open span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.menu-toggle.open span:nth-child(2) { opacity: 0; transform: scaleX(0); }
.menu-toggle.open span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* ─────────────────────────────────────────────
   SIDEBAR OVERLAY (dimmed backdrop on mobile)
   ───────────────────────────────────────────── */
.sidebar-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.45);
  z-index: 198;
  backdrop-filter: blur(2px);
  -webkit-backdrop-filter: blur(2px);
}
.sidebar-overlay.open { display: block; }

/* ─────────────────────────────────────────────
   DRAWER CLOSE BUTTON
   Shown inside the sidebar on mobile only
   ───────────────────────────────────────────── */
.sidebar-close {
  display: none;
  align-items: center;
  justify-content: space-between;
  padding: 12px 16px;
  border-bottom: 1px solid var(--border);
  margin-bottom: 4px;
  flex-shrink: 0;
}
.sidebar-close span {
  font-size: 12px;
  font-weight: 700;
  letter-spacing: .08em;
  text-transform: uppercase;
  color: var(--dim);
}
.sidebar-close button {
  background: none;
  border: none;
  cursor: pointer;
  color: var(--muted);
  font-size: 18px;
  line-height: 1;
  padding: 4px 7px;
  border-radius: 4px;
  transition: all .12s;
}
.sidebar-close button:hover { color: var(--text); background: var(--border); }

/* ─────────────────────────────────────────────
   TABLET  ≤ 1024px
   ───────────────────────────────────────────── */
@media (max-width: 1024px) {
  .main { padding: 40px 44px 80px; }
  .sidebar { width: 240px; }
  .lesson h2 { font-size: clamp(1.7rem, 2.8vw, 2.4rem); }
}

/* ─────────────────────────────────────────────
   MOBILE  ≤ 860px
   ───────────────────────────────────────────── */
@media (max-width: 860px) {

  /* Header */
  header { padding: 0 16px; }
  .prog-track { width: 80px; }
  .menu-toggle { display: flex; }

  /* Sidebar → slide-in drawer */
  .sidebar {
    display: flex;
    flex-direction: column;
    position: fixed;
    top: 0;
    left: 0;
    bottom: 0;
    width: min(280px, 85vw);
    z-index: 199;
    transform: translateX(-100%);
    transition: transform .28s cubic-bezier(.4, 0, .2, 1);
    box-shadow: none;
    overflow-y: auto;
    padding-top: 0;
  }
  .sidebar.open {
    transform: translateX(0);
    box-shadow: 6px 0 28px rgba(0, 0, 0, 0.15);
  }
  .sidebar-close { display: flex; }

  /* Main content */
  .main { padding: 28px 18px 80px; }
  .lesson h2 { font-size: clamp(1.5rem, 5vw, 2rem); }
  .lesson-intro { font-size: .92rem; }

  /* Nav prev/next — stack vertically, full width */
  .lesson-nav {
    flex-direction: column;
    align-items: stretch;
    gap: 10px;
  }
  .lesson-nav .btn {
    width: 100%;
    text-align: center;
    padding: 13px 20px;
    font-size: 14px;
  }

  /* Concept grid single column */
  .grid-2 { grid-template-columns: 1fr; }

  /* Quiz */
  .quiz { padding: 18px; }
  .quiz-opt { font-size: .87rem; padding: 10px 13px; }

  /* Code */
  pre { font-size: .79rem; line-height: 1.75; }

  /* Callout */
  .callout { padding: 13px 15px; font-size: .9rem; }

  /* Challenge */
  .challenge { padding: 18px; }

  /* Real-world banner */
  .rw-banner { flex-direction: column; gap: 8px; }

  /* Tables scroll */
  .tbl-wrap { -webkit-overflow-scrolling: touch; }
}

/* ─────────────────────────────────────────────
   SMALL PHONE  ≤ 480px
   ───────────────────────────────────────────── */
@media (max-width: 480px) {
  header { height: 52px; }
  .logo-text { font-size: 13px; }
  .badge { display: none; }
  .prog-track { width: 60px; }
  .main { padding: 20px 14px 80px; }
  .lesson h2 { font-size: 1.4rem; }
  pre { font-size: .73rem; }
  .quiz { padding: 14px; }
  .step { padding: 12px 0; }
  .callout { padding: 11px 13px; }
  .rw-banner { padding: 14px 16px; }
}
/* 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;
    }
}