/* ===========================================================
   GenAI Exam Prep — Shared Stylesheet
   Theme: White + Orange  |  Consistent design system
   =========================================================== */

@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700;800&family=JetBrains+Mono:wght@400;500;600&display=swap');

:root {
  --orange:        #EA580C;
  --orange-dark:   #C2410C;
  --orange-deep:   #9A3412;
  --orange-light:  #FB923C;
  --orange-pale:   #FFF4EA;
  --orange-pale2:  #FFE9D6;
  --orange-border: #FDBA8C;

  --bg:        #FFFFFF;
  --bg-warm:   #FFFBF7;
  --bg-soft:   #FFF8F2;
  --surface:   #FFFFFF;

  --text:      #292524;
  --text-mid:  #57534E;
  --text-soft: #78716C;

  --line:      #EDE6DF;
  --line-soft: #F3EEE9;

  --code-bg:   #1E1E2E;
  --code-head: #15151F;
  --code-text: #E4E4EF;
  --out-bg:    #11131A;

  --green:     #15803D;
  --green-bg:  #ECFDF3;
  --green-bd:  #A7F3C9;
  --red:       #B91C1C;
  --red-bg:    #FEF2F2;
  --red-bd:    #FCC8C8;
  --blue:      #1D4ED8;
  --blue-bg:   #EFF4FF;
  --blue-bd:   #C3D4FB;
  --purple:    #7C3AED;
  --purple-bg: #FAF5FF;
  --purple-bd: #E2CFFB;
  --coding-bg: #F3E8FF;
  --amber:     #B45309;
  --amber-bg:  #FFFBEB;
  --amber-bd:  #FCE8A8;

  --sidebar-w: 286px;
  --radius:    12px;
  --shadow:    0 1px 3px rgba(60,40,20,.07), 0 8px 24px rgba(60,40,20,.06);
  --shadow-sm: 0 1px 2px rgba(60,40,20,.08);
}

/* ===========================================================
   DARK THEME  (light is default; activated by data-theme="dark")
   =========================================================== */
[data-theme="dark"] {
  --orange:        #F97316;
  --orange-dark:   #FDBA74;
  --orange-deep:   #FDBA74;
  --orange-light:  #FB923C;
  --orange-pale:   #2C1D10;
  --orange-pale2:  #3D2A17;
  --orange-border: #5E3D20;

  --bg:        #14151A;
  --bg-warm:   #101116;
  --bg-soft:   #1C1D25;
  --surface:   #1B1C23;

  --text:      #E9E7E3;
  --text-mid:  #ADA9A1;
  --text-soft: #847F77;

  --line:      #2D2E38;
  --line-soft: #24252D;

  --green:     #4ADE80;
  --green-bg:  #14241B;
  --green-bd:  #2E5139;
  --red:       #F87171;
  --red-bg:    #2A1719;
  --red-bd:    #58292C;
  --blue:      #93B4FD;
  --blue-bg:   #151B2C;
  --blue-bd:   #2D3B5E;
  --purple:    #C4A5F5;
  --purple-bg: #1E1830;
  --purple-bd: #3B2F56;
  --coding-bg: #281C3A;
  --amber:     #FBBF24;
  --amber-bg:  #241D0C;
  --amber-bd:  #463819;

  --shadow:    0 1px 3px rgba(0,0,0,.45), 0 10px 26px rgba(0,0,0,.4);
  --shadow-sm: 0 1px 2px rgba(0,0,0,.45);
}

html { color-scheme: light; }
[data-theme="dark"] { color-scheme: dark; }

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

html { scroll-behavior: smooth; scroll-padding-top: 84px; }

body {
  font-family: 'Inter', -apple-system, 'Segoe UI', Roboto, sans-serif;
  background: var(--bg-warm);
  color: var(--text);
  line-height: 1.7;
  font-size: 16.5px;
  -webkit-font-smoothing: antialiased;
}

/* ---------- Scroll progress bar ---------- */
#progress-bar {
  position: fixed; top: 0; left: 0; height: 3px; width: 0%;
  background: linear-gradient(90deg, var(--orange-light), var(--orange));
  z-index: 1000; transition: width .1s linear;
}

/* ---------- Top bar ---------- */
.topbar {
  position: fixed; top: 0; left: 0; right: 0; height: 60px;
  background: var(--surface); border-bottom: 1px solid var(--line);
  display: flex; align-items: center; gap: 14px;
  padding: 0 20px; z-index: 900;
}
.topbar .brand {
  display: flex; align-items: center; gap: 10px;
  font-weight: 800; font-size: 1.05rem; color: var(--text);
  text-decoration: none; letter-spacing: -.02em;
}
.topbar .brand .logo {
  width: 32px; height: 32px; border-radius: 9px;
  background: linear-gradient(135deg, var(--orange), var(--orange-light));
  display: flex; align-items: center; justify-content: center;
  color: #fff; font-weight: 800; font-size: .95rem; flex-shrink: 0;
}
.topbar .brand .logo svg { width: 18px; height: 18px; }
.topbar .spacer { flex: 1; }
.topbar .top-link {
  text-decoration: none; color: var(--text-mid); font-weight: 600;
  font-size: .92rem; padding: 7px 13px; border-radius: 8px;
}
.topbar .top-link:hover { background: var(--orange-pale); color: var(--orange-dark); }
.topbar .top-link.exam {
  background: var(--orange); color: #fff;
}
.topbar .top-link.exam:hover { background: var(--orange-dark); }
.menu-btn {
  display: none; background: var(--orange-pale); border: 1px solid var(--orange-border);
  width: 38px; height: 38px; border-radius: 9px; cursor: pointer;
  color: var(--orange-dark); font-size: 1.2rem; align-items: center; justify-content: center;
}

/* ---------- Theme toggle ---------- */
.theme-btn {
  background: var(--bg-soft); border: 1px solid var(--line);
  width: 38px; height: 38px; border-radius: 9px; cursor: pointer;
  color: var(--text-mid); display: flex; align-items: center; justify-content: center;
  flex-shrink: 0; transition: background .15s, color .15s, border-color .15s;
}
.theme-btn:hover {
  background: var(--orange-pale); color: var(--orange-dark); border-color: var(--orange-border);
}
.theme-btn svg { width: 18px; height: 18px; }
.theme-btn .sun  { display: none; }
.theme-btn .moon { display: block; }
[data-theme="dark"] .theme-btn .sun  { display: block; }
[data-theme="dark"] .theme-btn .moon { display: none; }

/* ---------- Sidebar ---------- */
.sidebar {
  position: fixed; top: 60px; bottom: 0; left: 0; width: var(--sidebar-w);
  background: var(--surface); border-right: 1px solid var(--line);
  overflow-y: auto; padding: 18px 12px 60px; z-index: 800;
}
.sidebar::-webkit-scrollbar { width: 8px; }
.sidebar::-webkit-scrollbar-thumb { background: var(--orange-pale2); border-radius: 8px; }
.sidebar .nav-group { margin-bottom: 18px; }
.sidebar .nav-label {
  font-size: .72rem; font-weight: 700; text-transform: uppercase;
  letter-spacing: .09em; color: var(--text-soft); padding: 6px 12px;
}
.sidebar a.nav-item {
  display: flex; align-items: center; gap: 9px;
  text-decoration: none; color: var(--text-mid);
  padding: 8px 12px; border-radius: 8px; font-size: .9rem; font-weight: 500;
  margin-bottom: 1px; line-height: 1.35;
}
.sidebar a.nav-item:hover { background: var(--bg-soft); color: var(--orange-dark); }
.sidebar a.nav-item.active {
  background: var(--orange-pale); color: var(--orange-dark); font-weight: 700;
}
.sidebar a.nav-item .num {
  flex-shrink: 0; width: 24px; height: 24px; border-radius: 6px;
  background: var(--bg-soft); color: var(--text-soft);
  display: flex; align-items: center; justify-content: center;
  font-size: .76rem; font-weight: 700; font-family: 'JetBrains Mono', monospace;
}
.sidebar a.nav-item.active .num { background: var(--orange); color: #fff; }
.sidebar a.nav-item.special {
  background: var(--orange-pale); color: var(--orange-dark); font-weight: 700;
  border: 1px dashed var(--orange-border);
}
.sidebar a.nav-item.special:hover { background: var(--orange-pale2); }

/* ---------- Main layout ---------- */
.main {
  margin-left: var(--sidebar-w); margin-top: 60px;
  padding: 38px 46px 90px; max-width: 980px;
}
.content { max-width: 820px; }

/* ---------- Backdrop for mobile ---------- */
.backdrop {
  display: none; position: fixed; inset: 60px 0 0 0;
  background: rgba(40,25,10,.4); z-index: 790;
}

/* ---------- Lecture header ---------- */
.lec-tag {
  display: inline-flex; align-items: center; gap: 7px;
  background: var(--orange-pale); color: var(--orange-dark);
  font-weight: 700; font-size: .8rem; padding: 6px 13px;
  border-radius: 100px; letter-spacing: .03em; margin-bottom: 14px;
}
h1 {
  font-size: 2.3rem; font-weight: 800; letter-spacing: -.025em;
  line-height: 1.2; margin-bottom: 10px;
}
.lec-sub {
  font-size: 1.08rem; color: var(--text-mid); margin-bottom: 18px;
}
.lec-meta {
  display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 8px;
  padding-bottom: 22px; border-bottom: 2px solid var(--line);
}
.lec-meta .chip {
  background: var(--surface); border: 1px solid var(--line); border-radius: 100px;
  padding: 5px 12px; font-size: .8rem; font-weight: 600; color: var(--text-mid);
}
.lec-meta .chip b { color: var(--orange-dark); }

/* "In this lecture" box */
.toc-box {
  background: var(--bg-soft); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 18px 22px; margin: 26px 0;
}
.toc-box h4 {
  font-size: .82rem; text-transform: uppercase; letter-spacing: .07em;
  color: var(--orange-dark); margin-bottom: 10px;
}
.toc-box ol { list-style: none; counter-reset: toc; }
.toc-box ol li { counter-increment: toc; padding: 3px 0; }
.toc-box ol li a {
  text-decoration: none; color: var(--text-mid); font-weight: 500; font-size: .94rem;
}
.toc-box ol li a:hover { color: var(--orange); }
.toc-box ol li a::before {
  content: counter(toc); display: inline-flex; width: 20px; height: 20px;
  background: var(--orange-pale2); color: var(--orange-dark);
  border-radius: 5px; font-size: .72rem; font-weight: 700;
  align-items: center; justify-content: center; margin-right: 9px;
  font-family: 'JetBrains Mono', monospace;
}

/* ---------- Typography ---------- */
h2 {
  font-size: 1.62rem; font-weight: 800; letter-spacing: -.02em;
  margin: 46px 0 14px; padding-top: 14px; line-height: 1.25;
}
h2 .h-num {
  color: var(--orange); font-family: 'JetBrains Mono', monospace;
  font-size: 1.15rem; margin-right: 8px;
}
h3 {
  font-size: 1.22rem; font-weight: 700; margin: 30px 0 10px;
  letter-spacing: -.01em; color: var(--orange-deep);
}
h4 { font-size: 1.03rem; font-weight: 700; margin: 20px 0 8px; }

p { margin-bottom: 14px; }
.content ul, .content ol { margin: 0 0 16px 26px; }
.content li { margin-bottom: 7px; }
.content ul li::marker { color: var(--orange); }
.content ol li::marker { color: var(--orange); font-weight: 700; }

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

strong, b { font-weight: 700; color: var(--text); }
em { color: var(--orange-deep); font-style: italic; }

code {
  font-family: 'JetBrains Mono', monospace; font-size: .87em;
  background: var(--orange-pale); color: var(--orange-deep);
  padding: 2px 6px; border-radius: 5px; font-weight: 500;
}

hr { border: none; border-top: 1px solid var(--line); margin: 34px 0; }

/* ---------- Callout boxes ---------- */
.box {
  border-radius: var(--radius); padding: 16px 18px 16px 48px;
  margin: 20px 0; position: relative; font-size: .96rem;
}
.box .box-ic {
  position: absolute; left: 14px; top: 16px; font-size: 1.15rem;
  width: 22px; text-align: center;
}
.box p:last-child { margin-bottom: 0; }
.box .box-title { font-weight: 700; display: block; margin-bottom: 3px; }

.tip       { background: var(--orange-pale); border: 1px solid var(--orange-border); }
.tip .box-title { color: var(--orange-dark); }
.example   { background: var(--blue-bg); border: 1px solid var(--blue-bd); }
.example .box-title { color: var(--blue); }
.warning   { background: var(--red-bg); border: 1px solid var(--red-bd); }
.warning .box-title { color: var(--red); }
.keyidea   { background: var(--green-bg); border: 1px solid var(--green-bd); }
.keyidea .box-title { color: var(--green); }
.analogy   { background: var(--purple-bg); border: 1px solid var(--purple-bd); }
.analogy .box-title { color: var(--purple); }
.exam-note { background: var(--amber-bg); border: 1px solid var(--amber-bd); }
.exam-note .box-title { color: var(--amber); }

/* ---------- Definition card ---------- */
.defn {
  background: var(--surface); border: 1px solid var(--line); border-left: 4px solid var(--orange);
  border-radius: 10px; padding: 14px 18px; margin: 18px 0; box-shadow: var(--shadow-sm);
}
.defn .defn-term { font-weight: 800; color: var(--orange-dark); }

/* ---------- Formula block ---------- */
.formula {
  background: var(--bg-soft); border: 1px solid var(--line);
  border-radius: 10px; padding: 16px 20px; margin: 18px 0;
  text-align: center; font-family: 'JetBrains Mono', monospace;
  font-size: 1.05rem; color: var(--text); overflow-x: auto;
}
.formula .fnote {
  display: block; font-family: 'Inter', sans-serif; font-size: .82rem;
  color: var(--text-soft); margin-top: 8px;
}
.formula b { color: var(--orange-dark); }

/* ---------- Code blocks ---------- */
.code {
  border-radius: 10px; overflow: hidden; margin: 18px 0;
  box-shadow: var(--shadow); border: 1px solid #2A2A3C;
}
.code .code-head {
  background: var(--code-head); color: #9CA3B8;
  font-family: 'JetBrains Mono', monospace; font-size: .76rem;
  padding: 8px 14px; display: flex; align-items: center; gap: 8px;
  letter-spacing: .04em; text-transform: uppercase; font-weight: 600;
}
.code .code-head .dot { width: 11px; height: 11px; border-radius: 50%; }
.code .code-head .d1 { background: #FF5F56; }
.code .code-head .d2 { background: #FFBD2E; }
.code .code-head .d3 { background: #27C93F; }
.code .code-head .lang { margin-left: 6px; }
.code pre {
  background: var(--code-bg); color: var(--code-text);
  padding: 15px 16px; overflow-x: auto;
  font-family: 'JetBrains Mono', monospace; font-size: .85rem; line-height: 1.65;
}
.code pre::-webkit-scrollbar { height: 8px; }
.code pre::-webkit-scrollbar-thumb { background: #3A3A4E; border-radius: 8px; }
.code .output {
  background: var(--out-bg); border-top: 1px solid #2A2A3C;
  padding: 11px 16px; color: #B8E6C8;
  font-family: 'JetBrains Mono', monospace; font-size: .82rem;
  white-space: pre-wrap; line-height: 1.6;
}
.code .output .out-label {
  display: block; color: #6B7280; font-size: .68rem; text-transform: uppercase;
  letter-spacing: .08em; margin-bottom: 5px; font-weight: 600;
}
/* simple python syntax highlight */
.code .kw  { color: #FF9D7A; }
.code .str { color: #B8E6C8; }
.code .com { color: #6B7280; font-style: italic; }
.code .num { color: #F2C97D; }
.code .fn  { color: #82AAFF; }
.code .bi  { color: #C792EA; }

/* ---------- Tables ---------- */
.table-wrap { overflow-x: auto; margin: 20px 0; }
table {
  width: 100%; border-collapse: collapse; font-size: .9rem;
  background: var(--surface); border-radius: 10px; overflow: hidden;
  box-shadow: var(--shadow-sm); border: 1px solid var(--line);
}
thead th {
  background: var(--orange); color: #fff; text-align: left;
  padding: 10px 14px; font-weight: 600; font-size: .85rem;
}
tbody td { padding: 9px 14px; border-top: 1px solid var(--line-soft); vertical-align: top; }
tbody tr:nth-child(even) { background: var(--bg-soft); }
tbody tr:hover { background: var(--orange-pale); }
table code { background: var(--orange-pale2); }

/* ---------- Question cards ---------- */
.q-section-title {
  display: flex; align-items: center; gap: 10px;
  margin: 44px 0 6px; font-size: 1.4rem; font-weight: 800;
}
.q-section-title .qs-ic {
  width: 34px; height: 34px; border-radius: 9px;
  background: var(--orange); color: #fff; display: flex;
  align-items: center; justify-content: center; font-size: 1.05rem;
}
.q-section-sub { color: var(--text-mid); margin-bottom: 18px; font-size: .95rem; }

.qcard {
  background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  margin: 14px 0; box-shadow: var(--shadow-sm); overflow: hidden;
}
.qcard .qhead {
  display: flex; align-items: center; gap: 9px;
  padding: 11px 16px; background: var(--bg-soft); border-bottom: 1px solid var(--line-soft);
}
.qbadge {
  font-size: .68rem; font-weight: 700; text-transform: uppercase;
  letter-spacing: .05em; padding: 3px 9px; border-radius: 5px;
}
.qbadge.mcq    { background: var(--blue-bg); color: var(--blue); }
.qbadge.coding { background: var(--coding-bg); color: var(--purple); }
.qbadge.short  { background: var(--green-bg); color: var(--green); }
.qbadge.numerical { background: var(--orange-pale); color: var(--orange-dark); }
.qnum { font-weight: 800; color: var(--text); font-size: .9rem; }
.qhead .qtopic {
  margin-left: auto; font-size: .76rem; color: var(--text-soft); font-weight: 600;
}
.qbody { padding: 15px 16px; }
.qtext { font-weight: 600; margin-bottom: 12px; }
.qtext code { font-weight: 500; }

.qoptions { list-style: none; margin: 0 0 12px 0 !important; }
.qopt {
  display: flex; align-items: flex-start; gap: 10px;
  padding: 9px 13px; border: 1.5px solid var(--line); border-radius: 9px;
  margin-bottom: 7px !important; cursor: pointer; font-size: .92rem;
  transition: background .12s, border-color .12s;
}
.qopt:hover { border-color: var(--orange-border); background: var(--bg-soft); }
.qopt .opt-key {
  flex-shrink: 0; width: 22px; height: 22px; border-radius: 6px;
  background: var(--bg-soft); color: var(--text-mid);
  display: flex; align-items: center; justify-content: center;
  font-weight: 700; font-size: .78rem;
}
.qopt.selected { border-color: var(--orange); background: var(--orange-pale); }
.qopt.selected .opt-key { background: var(--orange); color: #fff; }

.qcard.revealed .qopt { cursor: default; }
.qcard.revealed .qopt[data-correct="true"] {
  border-color: var(--green); background: var(--green-bg);
}
.qcard.revealed .qopt[data-correct="true"] .opt-key { background: var(--green); color: #fff; }
.qcard.revealed .qopt.selected[data-correct="false"] {
  border-color: var(--red); background: var(--red-bg);
}
.qcard.revealed .qopt.selected[data-correct="false"] .opt-key { background: var(--red); color: #fff; }
.qcard.revealed .qopt[data-correct="true"] .opt-key::after { content: " ✓"; }

.qcheck {
  background: var(--orange); color: #fff; border: none;
  padding: 8px 18px; border-radius: 8px; font-weight: 700; font-size: .85rem;
  cursor: pointer; font-family: inherit;
}
.qcheck:hover { background: var(--orange-dark); }

.qexplain {
  display: none; margin-top: 13px; padding: 14px 16px;
  background: var(--bg-soft); border: 1px solid var(--line);
  border-left: 3px solid var(--orange); border-radius: 8px; font-size: .92rem;
}
.qcard.revealed .qexplain { display: block; }
.qexplain .ans-tag {
  display: inline-block; font-weight: 800; color: var(--green);
  font-size: .8rem; text-transform: uppercase; letter-spacing: .04em; margin-bottom: 4px;
}
.qexplain .code { margin: 10px 0; }
.qexplain p:last-child { margin-bottom: 0; }

/* ---------- Prev / Next nav ---------- */
.pagenav {
  display: flex; gap: 14px; margin-top: 50px;
  padding-top: 26px; border-top: 2px solid var(--line);
}
.pagenav a {
  flex: 1; text-decoration: none; padding: 14px 18px;
  border: 1px solid var(--line); border-radius: var(--radius);
  background: var(--surface); transition: border-color .15s, box-shadow .15s;
}
.pagenav a:hover { border-color: var(--orange); box-shadow: var(--shadow); }
.pagenav a .pn-dir {
  font-size: .74rem; color: var(--text-soft); font-weight: 700;
  text-transform: uppercase; letter-spacing: .06em;
}
.pagenav a .pn-title { font-weight: 700; color: var(--orange-dark); margin-top: 3px; }
.pagenav a.next { text-align: right; }
.pagenav a.disabled { opacity: .4; pointer-events: none; }

/* ---------- Back to top ---------- */
#to-top {
  position: fixed; bottom: 26px; right: 26px; width: 44px; height: 44px;
  background: var(--orange); color: #fff; border: none; border-radius: 11px;
  font-size: 1.2rem; cursor: pointer; display: none; z-index: 850;
  box-shadow: var(--shadow); align-items: center; justify-content: center;
}
#to-top:hover { background: var(--orange-dark); }

/* ===========================================================
   HOMEPAGE
   =========================================================== */
.hero {
  background: linear-gradient(135deg, var(--surface) 0%, var(--orange-pale) 100%);
  border: 1px solid var(--orange-border); border-radius: 18px;
  padding: 40px 40px; margin-bottom: 30px;
}
.hero .hero-tag {
  display: inline-block; background: var(--orange); color: #fff;
  font-size: .76rem; font-weight: 700; padding: 5px 13px;
  border-radius: 100px; letter-spacing: .04em; margin-bottom: 14px;
}
.hero h1 { font-size: 2.6rem; margin-bottom: 12px; }
.hero h1 .hl { color: var(--orange); }
.hero p { font-size: 1.1rem; color: var(--text-mid); max-width: 620px; }
.hero .hero-actions { margin-top: 22px; display: flex; gap: 12px; flex-wrap: wrap; }
.btn {
  text-decoration: none; font-weight: 700; font-size: .92rem;
  padding: 12px 22px; border-radius: 10px; display: inline-flex; align-items: center; gap: 8px;
}
.btn.primary { background: var(--orange); color: #fff; }
.btn.primary:hover { background: var(--orange-dark); }
.btn.ghost { background: var(--surface); color: var(--orange-dark); border: 1px solid var(--orange-border); }
.btn.ghost:hover { background: var(--orange-pale); }

.stat-row {
  display: grid; grid-template-columns: repeat(4, 1fr); gap: 14px; margin: 26px 0 36px;
}
.stat {
  background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 16px 18px; text-align: center;
}
.stat .s-num { font-size: 1.9rem; font-weight: 800; color: var(--orange); line-height: 1; }
.stat .s-lab { font-size: .82rem; color: var(--text-mid); margin-top: 6px; font-weight: 600; }

.unit-title {
  font-size: .8rem; font-weight: 700; text-transform: uppercase;
  letter-spacing: .08em; color: var(--orange-dark);
  margin: 32px 0 12px; display: flex; align-items: center; gap: 10px;
}
.unit-title::after { content: ""; flex: 1; height: 1px; background: var(--line); }

.lec-grid {
  display: grid; grid-template-columns: repeat(2, 1fr); gap: 14px;
}
.lec-card {
  text-decoration: none; background: var(--surface); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 16px 18px; display: block;
  transition: border-color .15s, box-shadow .15s, transform .15s;
}
.lec-card:hover {
  border-color: var(--orange); box-shadow: var(--shadow); transform: translateY(-2px);
}
.lec-card .lc-top { display: flex; align-items: center; gap: 10px; margin-bottom: 8px; }
.lec-card .lc-num {
  width: 32px; height: 32px; border-radius: 8px; flex-shrink: 0;
  background: linear-gradient(135deg, var(--orange), var(--orange-light));
  color: #fff; font-weight: 800; font-size: .85rem;
  display: flex; align-items: center; justify-content: center;
  font-family: 'JetBrains Mono', monospace;
}
.lec-card .lc-title { font-weight: 700; color: var(--text); font-size: 1rem; line-height: 1.3; }
.lec-card .lc-desc { font-size: .87rem; color: var(--text-mid); }
.lec-card .lc-tags { margin-top: 10px; display: flex; flex-wrap: wrap; gap: 5px; }
.lec-card .lc-tag {
  font-size: .72rem; background: var(--bg-soft); color: var(--text-soft);
  padding: 3px 8px; border-radius: 5px; font-weight: 600;
}

/* how to use list */
.howto {
  background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 8px 4px; margin: 14px 0;
}
.howto .ht-item { display: flex; gap: 14px; padding: 14px 18px; }
.howto .ht-item + .ht-item { border-top: 1px solid var(--line-soft); }
.howto .ht-ic {
  flex-shrink: 0; width: 38px; height: 38px; border-radius: 9px;
  background: var(--orange-pale); color: var(--orange-dark);
  display: flex; align-items: center; justify-content: center; font-size: 1.2rem;
}
.howto .ht-item h4 { margin: 2px 0 3px; }
.howto .ht-item p { margin: 0; font-size: .9rem; color: var(--text-mid); }

/* ---------- Footer ---------- */
.foot {
  margin-top: 40px; padding-top: 22px; border-top: 1px solid var(--line);
  font-size: .85rem; color: var(--text-soft);
}
.foot .made-by strong, .site-foot .made-by strong { color: var(--orange-dark); font-weight: 800; }

/* ---------- Sidebar credit ---------- */
.sidebar-credit {
  margin: 16px 12px 0; padding: 14px 4px 6px;
  border-top: 1px solid var(--line);
  font-size: .76rem; color: var(--text-soft); line-height: 1.4;
}
.sidebar-credit .mb-name {
  display: block; margin-top: 2px; font-size: .92rem;
  font-weight: 800; color: var(--orange-dark); letter-spacing: -.01em;
}

/* ---------- Per-page footer credit ---------- */
.site-foot {
  margin-top: 30px; padding-top: 6px; text-align: center;
  font-size: .85rem; color: var(--text-soft);
}
.site-foot .made-by strong { color: var(--orange-dark); font-weight: 800; }

/* ===========================================================
   MOCK EXAM
   =========================================================== */
.exam-panel {
  position: sticky; top: 74px; z-index: 500;
  background: var(--surface); border: 1px solid var(--orange-border);
  border-radius: var(--radius); padding: 14px 18px; margin-bottom: 24px;
  box-shadow: var(--shadow); display: flex; align-items: center; gap: 14px; flex-wrap: wrap;
}
.exam-panel .ep-score {
  font-weight: 800; font-size: 1.05rem; color: var(--orange-dark);
}
.exam-panel .ep-bar {
  flex: 1; min-width: 120px; height: 10px; background: var(--bg-soft);
  border-radius: 100px; overflow: hidden;
}
.exam-panel .ep-fill {
  height: 100%; width: 0%; background: linear-gradient(90deg, var(--orange-light), var(--orange));
  transition: width .4s;
}
.exam-result {
  display: none; margin-top: 10px; font-weight: 600; font-size: .92rem;
}

/* ---------- Misc ---------- */
.spacer-lg { height: 30px; }
.center { text-align: center; }
.muted { color: var(--text-soft); font-size: .9rem; }

/* ===========================================================
   RESPONSIVE
   =========================================================== */
@media (max-width: 1100px) {
  .main { padding: 32px 30px 80px; }
  .lec-grid, .stat-row { gap: 12px; }
}
@media (max-width: 920px) {
  .menu-btn { display: flex; }
  .sidebar {
    transform: translateX(-100%); transition: transform .25s ease;
    box-shadow: var(--shadow);
  }
  .sidebar.open { transform: translateX(0); }
  .backdrop.show { display: block; }
  .main { margin-left: 0; padding: 26px 20px 70px; }
  .stat-row { grid-template-columns: repeat(2, 1fr); }
  .lec-grid { grid-template-columns: 1fr; }
  .tool-grid { grid-template-columns: 1fr; }
  .cheat-grid { columns: 1; }
  h1 { font-size: 1.9rem; }
  .hero { padding: 28px 24px; }
  .hero h1 { font-size: 2rem; }
  .pagenav { flex-direction: column; }
}
@media (max-width: 560px) {
  body { font-size: 16px; }
  .topbar { padding: 0 14px; }
  .topbar .brand span.full { display: none; }
  .main { padding: 22px 16px 60px; }
  h2 { font-size: 1.4rem; }
  .box { padding: 14px 14px 14px 44px; }
  .fc-face { padding: 44px 18px 32px; }
  .fc-q { font-size: 1.05rem; }
}
@media print {
  .cheat-grid { columns: 2; }
  .fc-card, .theme-btn { display: none !important; }
}

/* ===========================================================
   EXAM TOOLKIT — shared
   =========================================================== */
.tool-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 14px; margin: 16px 0; }
.tool-card {
  text-decoration: none; background: var(--surface); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 18px; display: flex; gap: 14px;
  transition: border-color .15s, box-shadow .15s, transform .15s;
}
.tool-card:hover { border-color: var(--orange); box-shadow: var(--shadow); transform: translateY(-2px); }
.tool-card .tc-ic {
  flex-shrink: 0; width: 46px; height: 46px; border-radius: 11px;
  background: linear-gradient(135deg, var(--orange), var(--orange-light));
  color: #fff; display: flex; align-items: center; justify-content: center; font-size: 1.35rem;
}
.tool-card .tc-title { font-weight: 700; color: var(--text); font-size: 1.04rem; }
.tool-card .tc-desc { font-size: .87rem; color: var(--text-mid); margin-top: 3px; }

/* ---------- Cheat Sheet ---------- */
.cheat-grid { columns: 2; column-gap: 18px; margin: 22px 0; }
.cheat-card {
  break-inside: avoid; -webkit-column-break-inside: avoid;
  background: var(--surface); border: 1px solid var(--line);
  border-radius: 11px; margin: 0 0 18px; overflow: hidden; box-shadow: var(--shadow-sm);
}
.cheat-card > h4 {
  margin: 0; padding: 9px 13px; font-size: .88rem; font-weight: 700;
  background: var(--orange-pale); color: var(--orange-dark);
  display: flex; align-items: center; gap: 8px;
}
.cheat-card .cc-num {
  font-family: 'JetBrains Mono', monospace; font-size: .68rem; font-weight: 700;
  background: var(--orange); color: #fff; border-radius: 5px; padding: 1px 6px; flex-shrink: 0;
}
.cheat-card .cc-body { padding: 10px 13px 12px; font-size: .85rem; line-height: 1.6; }
.cheat-card .cc-body p { margin: 0 0 6px; }
.cheat-card .cc-body ul { margin: 4px 0 8px 17px; }
.cheat-card .cc-body li { margin-bottom: 4px; }
.cheat-card .cc-body li::marker { color: var(--orange); }
.cheat-card .cc-body strong { color: var(--orange-deep); }
.cheat-card .cf {
  font-family: 'JetBrains Mono', monospace; font-size: .8rem;
  background: var(--bg-soft); border: 1px solid var(--line);
  border-radius: 6px; padding: 5px 9px; margin: 6px 0; display: block; line-height: 1.5;
}
.cheat-card .cf b { color: var(--orange-dark); }
.cheat-intro {
  display: flex; flex-wrap: wrap; gap: 8px; margin: 4px 0 6px;
}

/* ---------- Flashcards ---------- */
.fc-wrap { max-width: 660px; margin: 24px auto 0; }
.fc-toolbar { display: flex; flex-wrap: wrap; gap: 10px; align-items: center; margin-bottom: 12px; }
.fc-select {
  font-family: inherit; font-size: .86rem; font-weight: 600;
  padding: 8px 12px; border-radius: 9px; border: 1px solid var(--line);
  background: var(--surface); color: var(--text); cursor: pointer;
}
.fc-btn {
  font-family: inherit; font-size: .84rem; font-weight: 700; cursor: pointer;
  padding: 8px 14px; border-radius: 9px; border: 1px solid var(--orange-border);
  background: var(--orange-pale); color: var(--orange-dark);
}
.fc-btn:hover { background: var(--orange-pale2); }
.fc-progress { margin-left: auto; font-weight: 700; font-size: .85rem; color: var(--text-mid); }
.fc-bar { height: 8px; background: var(--bg-soft); border-radius: 100px; overflow: hidden; margin-bottom: 18px; border: 1px solid var(--line); }
.fc-bar-fill { height: 100%; width: 0%; background: linear-gradient(90deg, var(--orange-light), var(--orange)); transition: width .35s; }

.fc-stage { perspective: 1600px; }
.fc-card {
  position: relative; width: 100%; min-height: 310px;
  transform-style: preserve-3d; transition: transform .55s cubic-bezier(.2,.8,.2,1);
  cursor: pointer;
}
.fc-card.flipped { transform: rotateY(180deg); }
.fc-face {
  position: absolute; inset: 0; backface-visibility: hidden; -webkit-backface-visibility: hidden;
  border-radius: 16px; border: 1px solid var(--line); box-shadow: var(--shadow);
  padding: 46px 28px 34px; display: flex; flex-direction: column; justify-content: center;
  overflow: auto;
}
.fc-front { background: var(--surface); }
.fc-back  { background: var(--orange-pale); transform: rotateY(180deg); }
.fc-tag {
  position: absolute; top: 14px; left: 14px; font-size: .66rem; font-weight: 800;
  text-transform: uppercase; letter-spacing: .06em; color: var(--orange-dark);
  background: var(--bg-soft); padding: 3px 9px; border-radius: 6px;
}
.fc-corner { position: absolute; top: 14px; right: 16px; font-size: .72rem; color: var(--text-soft); font-weight: 600; }
.fc-hint { position: absolute; bottom: 12px; left: 0; right: 0; text-align: center; font-size: .72rem; color: var(--text-soft); }
.fc-q { font-size: 1.2rem; font-weight: 700; line-height: 1.45; text-align: center; }
.fc-a { font-size: 1rem; line-height: 1.62; }
.fc-a code { font-size: .85em; }
.fc-actions { display: flex; gap: 10px; margin-top: 16px; }
.fc-actions button {
  flex: 1; padding: 11px 8px; border-radius: 10px; font-weight: 700;
  font-size: .88rem; cursor: pointer; font-family: inherit; border: 1px solid;
}
.fc-prev   { background: var(--surface); color: var(--text-mid); border-color: var(--line); }
.fc-prev:hover { background: var(--bg-soft); }
.fc-known  { background: var(--green-bg); color: var(--green); border-color: var(--green-bd); }
.fc-review { background: var(--orange); color: #fff; border-color: var(--orange); }
.fc-known:hover, .fc-review:hover { filter: brightness(.96); }
.fc-done {
  text-align: center; padding: 42px 24px; background: var(--surface);
  border: 1px solid var(--line); border-radius: 16px; box-shadow: var(--shadow-sm);
}
.fc-done .fc-done-num { font-size: 2.6rem; font-weight: 800; color: var(--orange); }

/* ---------- Trap / Truth cards ---------- */
.trap {
  background: var(--surface); border: 1px solid var(--line);
  border-radius: 12px; margin: 14px 0; overflow: hidden; box-shadow: var(--shadow-sm);
}
.trap .trap-topic {
  font-size: .72rem; color: var(--text-soft); font-weight: 700;
  text-transform: uppercase; letter-spacing: .05em; padding: 9px 16px 0;
}
.trap-row { padding: 11px 16px 13px; display: flex; gap: 11px; }
.trap-x { background: var(--red-bg); }
.trap-v { background: var(--green-bg); }
.trap-ic {
  flex-shrink: 0; width: 24px; height: 24px; border-radius: 6px;
  display: flex; align-items: center; justify-content: center;
  font-weight: 800; font-size: .92rem; color: #fff;
}
.trap-x .trap-ic { background: var(--red); }
.trap-v .trap-ic { background: var(--green); }
.trap-row .tr-label {
  font-weight: 800; font-size: .68rem; text-transform: uppercase;
  letter-spacing: .05em; display: block; margin-bottom: 2px;
}
.trap-x .tr-label { color: var(--red); }
.trap-v .tr-label { color: var(--green); }
.trap-row p { margin: 0; font-size: .92rem; line-height: 1.55; }

/* ---------- Code Patterns ---------- */
.cp-toc {
  display: flex; flex-wrap: wrap; gap: 7px; margin: 16px 0 8px;
}
.cp-toc a {
  text-decoration: none; font-size: .8rem; font-weight: 600;
  background: var(--surface); border: 1px solid var(--line);
  color: var(--text-mid); padding: 5px 11px; border-radius: 100px;
}
.cp-toc a:hover { border-color: var(--orange); color: var(--orange-dark); background: var(--orange-pale); }
.cp-item { margin: 16px 0; }
.cp-item .cp-desc { font-size: .92rem; color: var(--text-mid); margin: 0 0 7px; }
.cp-item .cp-desc b { color: var(--orange-deep); }

/* ---------- Print ---------- */
@media print {
  .topbar, .sidebar, #to-top, #progress-bar, .menu-btn, .pagenav, .backdrop { display: none !important; }
  .main { margin: 0; padding: 0; max-width: 100%; }
  .qexplain { display: block !important; }
  .code, .box, .qcard { box-shadow: none; }
}