/* main.css — Digital Finance Course Design System
   Replaces shared.css. All components use CSS custom properties.
   Dark mode overrides live in dark-mode.css (vars only, no component redeclarations).
   =========================================================================== */

/* === DESIGN TOKENS ======================================================== */
:root {
  /* Backgrounds */
  --bg:          #f6f8fa;
  --bg-card:     #ffffff;
  --bg-sub:      #f6f8fa;

  /* Text */
  --text:        #24292e;
  --text-muted:  #586069;

  /* Borders */
  --border:      #e1e4e8;
  --border-light:#f0f0f0;

  /* Brand accents */
  --link:        #0366d6;
  --link-hover:  #0550ae;
  --nav-bg:      #24292e;

  /* Version colors */
  --v3-accent:   #0366d6;
  --v3-bg:       #e3f2fd;
  --v3-text:     #0366d6;
  --v4-accent:   #6f42c1;
  --v4-bg:       #f3e8ff;
  --v4-text:     #6f42c1;
  --phd-accent:  #5b21b6;
  --phd-bg:      #ede9fe;
  --phd-text:    #5b21b6;
  --de-accent:   #5b2c8e;

  /* Semantic */
  --warning-bg:     #fffbeb;
  --warning-border: #fef3c7;
  --warning-text:   #92400e;
  --tag-bg:         #eff6ff;
  --tag-color:      #0366d6;
  --shadow:         rgba(0,0,0,0.10);

  /* Typography */
  --font:        -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif;
  --font-size:   13px;
  --lh:          1.45;

  /* Geometry */
  --radius:      6px;
  --radius-sm:   4px;
  --nav-h:       38px;
}

/* === RESET + BASE ========================================================== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

body {
  font-family: var(--font);
  font-size: var(--font-size);
  line-height: var(--lh);
  background: var(--bg);
  color: var(--text);
  transition: background-color 0.2s, color 0.2s;
}

a {
  color: var(--link);
  text-decoration: none;
  transition: color 0.15s;
}
a:hover { color: var(--link-hover); }

img { max-width: 100%; display: block; }

h1, h2, h3, h4 { line-height: 1.25; }

/* Skip-link for keyboard users */
.skip-link {
  position: absolute;
  top: -50px;
  left: 0;
  background: var(--link);
  color: #fff;
  padding: 10px 16px;
  z-index: 10000;
  text-decoration: none;
  font-weight: 600;
  font-size: 14px;
  border-radius: 0 0 var(--radius-sm) 0;
}
.skip-link:focus { top: 0; outline: 3px solid #fff; outline-offset: -3px; }

/* === FOCUS STYLES ========================================================== */
a:focus-visible,
button:focus-visible,
input:focus-visible,
select:focus-visible,
summary:focus-visible {
  outline: 2px solid var(--link);
  outline-offset: 2px;
  border-radius: var(--radius-sm);
}

/* === NAV =================================================================== */
.nav {
  background: var(--nav-bg);
  padding: 0 12px;
  height: var(--nav-h);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  position: sticky;
  top: 0;
  z-index: 100;
  border-bottom: 1px solid rgba(255,255,255,0.06);
}

.nav-title {
  color: #fff;
  font-weight: 600;
  font-size: 14px;
  white-space: nowrap;
  flex-shrink: 0;
}
.nav-title:hover { color: #fff; opacity: 0.9; }

.nav-links {
  display: flex;
  align-items: center;
  gap: 14px;
  flex-wrap: wrap;
}
.nav-links a {
  color: rgba(255,255,255,0.75);
  font-size: 11px;
}
.nav-links a:hover,
.nav-links a:focus-visible { color: #fff; outline-color: #fff; }

.nav-search {
  background: rgba(255,255,255,0.10);
  border: 1px solid rgba(255,255,255,0.18);
  border-radius: var(--radius-sm);
  color: #fff;
  font-size: 11px;
  padding: 3px 8px;
  width: 180px;
  transition: background 0.15s, border-color 0.15s;
}
.nav-search::placeholder { color: rgba(255,255,255,0.45); }
.nav-search:focus {
  outline: 2px solid rgba(255,255,255,0.5);
  outline-offset: 1px;
  background: rgba(255,255,255,0.15);
}

/* Dark mode toggle button (lives in nav) */
.dark-toggle {
  background: transparent;
  border: 1px solid rgba(255,255,255,0.28);
  color: #fff;
  padding: 3px 9px;
  border-radius: var(--radius-sm);
  font-size: 11px;
  cursor: pointer;
  white-space: nowrap;
  transition: background 0.15s, border-color 0.15s;
}
.dark-toggle:hover {
  background: rgba(255,255,255,0.10);
  border-color: rgba(255,255,255,0.50);
}

/* === LAYOUT ================================================================ */
.wrap {
  display: flex;
  max-width: 1800px;
  margin: 0 auto;
}

.main {
  flex: 1;
  min-width: 0;
  padding: 10px 12px;
}

/* === SIDEBAR =============================================================== */
.side {
  width: 188px;
  flex-shrink: 0;
  background: var(--bg-card);
  border-right: 1px solid var(--border);
  height: calc(100vh - var(--nav-h));
  overflow-y: auto;
  position: sticky;
  top: var(--nav-h);
  scrollbar-width: thin;
  scrollbar-color: var(--border) transparent;
}

.side-head {
  padding: 8px 10px;
  background: var(--bg-sub);
  border-bottom: 1px solid var(--border);
  font-weight: 600;
  font-size: 11px;
  color: var(--text);
  letter-spacing: 0.02em;
  text-transform: uppercase;
}

.side details { border-bottom: 1px solid var(--border-light); }

.side summary {
  padding: 6px 10px;
  font-size: 10px;
  font-weight: 600;
  cursor: pointer;
  list-style: none;
  display: flex;
  justify-content: space-between;
  align-items: center;
  color: var(--text);
  user-select: none;
}
.side summary::-webkit-details-marker { display: none; }
.side summary::after { content: "+"; color: var(--text-muted); font-size: 12px; }
.side details[open] summary::after { content: "−"; }
.side summary:hover { background: var(--bg-sub); }

.side a {
  display: block;
  padding: 4px 10px 4px 16px;
  font-size: 10px;
  color: var(--text);
  border-left: 2px solid transparent;
  transition: background 0.1s, border-color 0.1s, color 0.1s;
}
.side a:hover,
.side a:focus-visible {
  background: var(--bg-sub);
  border-left-color: var(--link);
  color: var(--link);
  outline-offset: -2px;
}
.side a.active {
  border-left-color: var(--link);
  color: var(--link);
  font-weight: 600;
  background: var(--tag-bg);
}

/* === HERO ================================================================== */
.hero {
  background: linear-gradient(135deg, #24292e 0%, #0366d6 100%);
  color: #fff;
  padding: 14px 18px;
  border-radius: var(--radius);
  margin-bottom: 12px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}
.hero h1,
.hero-left h1 { font-size: 18px; font-weight: 700; }
.hero p,
.hero-left p  { font-size: 11px; opacity: 0.82; margin-top: 3px; }

.hero-stats {
  display: flex;
  gap: 22px;
  flex-shrink: 0;
}
.hero-stats span { text-align: center; }
.hero-stats b    { display: block; font-size: 20px; font-weight: 700; }
.hero-stats small{ font-size: 9px; opacity: 0.70; }

/* === SECTION HEADS ========================================================= */
.section-head {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 8px;
  padding: 6px 0;
  border-bottom: 2px solid var(--border);
}
.section-head h2,
.section-head h3 { font-size: 13px; font-weight: 600; color: var(--text); }
.section-head span {
  width: 22px;
  height: 22px;
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  color: #fff;
  font-size: 11px;
  font-weight: 700;
  flex-shrink: 0;
}

/* === CARD GRID ============================================================= */
.card-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
  margin-bottom: 12px;
}

/* Legacy alias for existing pages */
.lgrid { display: grid; grid-template-columns: repeat(4,1fr); gap: 8px; margin-bottom: 12px; }

.card,
.lcard {
  display: block;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 12px 14px;
  color: var(--text);
  transition: border-color 0.15s, box-shadow 0.15s, transform 0.1s;
}
.card:hover,
.lcard:hover {
  border-color: var(--link);
  box-shadow: 0 2px 8px var(--shadow);
  transform: translateY(-1px);
}
.card:focus-visible,
.lcard:focus-visible {
  outline: 2px solid var(--link);
  outline-offset: 2px;
  border-color: var(--link);
}

/* Card sub-elements */
.card-num,
.lcard-num {
  display: inline-block;
  font-size: 10px;
  font-weight: 700;
  padding: 2px 6px;
  border-radius: 3px;
  margin-bottom: 6px;
  background: var(--tag-bg);
  color: var(--tag-color);
}
.card-title,
.lcard-title { font-size: 12px; font-weight: 600; color: var(--text); margin-bottom: 4px; }
.card-meta   { font-size: 10px; color: var(--text-muted); }

/* === VERSION CARDS (landing page chooser) ================================== */
.version-cards {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin-bottom: 16px;
}

.version-card {
  background: var(--bg-card);
  border: 2px solid var(--border);
  border-radius: var(--radius);
  padding: 20px 22px;
  transition: border-color 0.15s, box-shadow 0.15s, transform 0.1s;
  display: block;
  color: var(--text);
}
.version-card:hover {
  box-shadow: 0 4px 16px var(--shadow);
  transform: translateY(-2px);
}
.version-card.v3 { border-top: 4px solid var(--v3-accent); }
.version-card.v3:hover { border-color: var(--v3-accent); }
.version-card.v4 { border-top: 4px solid var(--v4-accent); }
.version-card.v4:hover { border-color: var(--v4-accent); }

.version-card h2 { font-size: 16px; font-weight: 700; margin-bottom: 6px; }
.version-card p  { font-size: 12px; color: var(--text-muted); line-height: 1.5; }
.version-card.v3 h2 { color: var(--v3-accent); }
.version-card.v4 h2 { color: var(--v4-accent); }

/* === TABLES ================================================================ */
.table {
  width: 100%;
  border-collapse: collapse;
  font-size: 12px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
}
.table th {
  background: var(--bg-sub);
  color: var(--text-muted);
  font-weight: 600;
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.03em;
  padding: 7px 10px;
  border-bottom: 1px solid var(--border);
  text-align: left;
}
.table td {
  padding: 6px 10px;
  border-bottom: 1px solid var(--border-light);
  color: var(--text);
  vertical-align: middle;
}
.table tbody tr:last-child td { border-bottom: none; }
.table tbody tr:hover { background: var(--bg-sub); }

/* Generic td/th fallback (non-.table tables) */
table  { width: 100%; border-collapse: collapse; background: var(--bg-card); border: 1px solid var(--border); }
th     { background: var(--bg-sub); color: var(--text-muted); font-size: 11px; font-weight: 600;
         text-transform: uppercase; letter-spacing: 0.03em; padding: 7px 10px;
         border-bottom: 1px solid var(--border); text-align: left; }
td     { padding: 6px 10px; border-bottom: 1px solid var(--border-light); color: var(--text); }
tr:hover { background: var(--bg-sub); }

/* === BUTTONS =============================================================== */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 5px 12px;
  border-radius: var(--radius-sm);
  font-size: 12px;
  font-weight: 500;
  cursor: pointer;
  text-decoration: none;
  border: 1px solid var(--border);
  background: var(--bg-card);
  color: var(--text);
  transition: background 0.15s, border-color 0.15s, box-shadow 0.15s;
  white-space: nowrap;
}
.btn:hover {
  background: var(--bg-sub);
  border-color: var(--text-muted);
  color: var(--text);
}

.btn-primary {
  background: var(--link);
  border-color: var(--link);
  color: #fff;
}
.btn-primary:hover {
  background: var(--link-hover);
  border-color: var(--link-hover);
  color: #fff;
}

.btn-outline {
  background: transparent;
  border-color: var(--link);
  color: var(--link);
}
.btn-outline:hover {
  background: var(--tag-bg);
  color: var(--link);
}

.btn-sm { padding: 3px 8px; font-size: 11px; }

/* === BADGES ================================================================ */
.badge {
  display: inline-block;
  padding: 2px 7px;
  border-radius: 20px;
  font-size: 10px;
  font-weight: 600;
  white-space: nowrap;
}
.badge-v3  { background: var(--v3-bg);  color: var(--v3-text); }
.badge-v4  { background: var(--v4-bg);  color: var(--v4-text); }
.badge-phd { background: var(--phd-bg); color: var(--phd-text); }

/* === TABS ================================================================== */
.tab-group {
  display: flex;
  gap: 2px;
  border-bottom: 2px solid var(--border);
  margin-bottom: 12px;
}
.tab-btn {
  padding: 6px 14px;
  font-size: 12px;
  font-weight: 500;
  cursor: pointer;
  border: none;
  background: none;
  color: var(--text-muted);
  border-bottom: 2px solid transparent;
  margin-bottom: -2px;
  border-radius: var(--radius-sm) var(--radius-sm) 0 0;
  transition: color 0.15s;
}
.tab-btn:hover { color: var(--text); background: var(--bg-sub); }
.tab-btn.active { color: var(--link); border-bottom-color: var(--link); font-weight: 600; }
.tab-content { display: none; }
.tab-content.active { display: block; }

/* === STATS GRID ============================================================ */
.stat-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(110px, 1fr));
  gap: 8px;
  margin-bottom: 12px;
}
.stat-box {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 10px 12px;
  text-align: center;
}
.stat-num   { font-size: 22px; font-weight: 700; color: var(--link); display: block; }
.stat-label { font-size: 10px; color: var(--text-muted); margin-top: 2px; display: block; }

/* === DOWNLOAD LINKS ======================================================== */
.dl-links {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin: 8px 0;
}
.dl-links a {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 4px 10px;
  font-size: 11px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--bg-card);
  color: var(--text);
  transition: background 0.15s, border-color 0.15s;
}
.dl-links a:hover {
  background: var(--bg-sub);
  border-color: var(--link);
  color: var(--link);
}

/* === INFO BOX ============================================================== */
.info-box {
  background: var(--tag-bg);
  border: 1px solid var(--link);
  border-left: 4px solid var(--link);
  border-radius: var(--radius-sm);
  padding: 10px 14px;
  font-size: 12px;
  color: var(--text);
  margin: 8px 0;
}
.info-box.warning {
  background: var(--warning-bg);
  border-color: var(--warning-border);
  border-left-color: #f59e0b;
  color: var(--warning-text);
}

/* Legacy aliases */
.info-box-info    { background: var(--tag-bg); border: 1px solid var(--link); border-left: 4px solid var(--link); border-radius: var(--radius-sm); padding: 10px 14px; font-size: 12px; color: var(--text); margin: 8px 0; }
.info-box-warning { background: var(--warning-bg); border: 1px solid var(--warning-border); border-left: 4px solid #f59e0b; border-radius: var(--radius-sm); padding: 10px 14px; font-size: 12px; color: var(--warning-text); margin: 8px 0; }

/* === LESSON NUMBER BADGE =================================================== */
.lesson-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 22px;
  height: 22px;
  padding: 0 5px;
  border-radius: var(--radius-sm);
  font-size: 10px;
  font-weight: 700;
  background: var(--tag-bg);
  color: var(--tag-color);
}
.lesson-num.v4 { background: var(--v4-bg); color: var(--v4-text); }
.lesson-num.phd { background: var(--phd-bg); color: var(--phd-text); }

/* === FOOTER ================================================================ */
.foot {
  text-align: center;
  padding: 14px 12px;
  font-size: 10px;
  color: var(--text-muted);
  border-top: 1px solid var(--border);
  margin-top: 16px;
}

/* === SECTION BOX (legacy component) ======================================== */
.section-box {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 14px;
  margin-bottom: 10px;
}

/* === PDF / PRESENTATION CARD =============================================== */
.card.pdf-link,
.pdf-link {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 4px 10px;
  background: var(--link);
  border: 1px solid var(--link);
  border-radius: var(--radius-sm);
  color: #fff;
  font-size: 11px;
  font-weight: 500;
  transition: background 0.15s;
}
.card.pdf-link:hover,
.pdf-link:hover { background: var(--link-hover); border-color: var(--link-hover); color: #fff; }

/* === GITHUB BUTTON ========================================================= */
.github-btn {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 5px 12px;
  background: var(--bg-sub);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  color: var(--text);
  font-size: 11px;
  font-weight: 500;
  cursor: pointer;
  transition: background 0.15s, border-color 0.15s;
}
.github-btn:hover { background: var(--bg-card); border-color: var(--text-muted); color: var(--text); }

/* === RESPONSIVE ============================================================ */
@media (max-width: 1400px) {
  .card-grid, .lgrid { grid-template-columns: repeat(3, 1fr); }
}

@media (max-width: 1000px) {
  .card-grid, .lgrid { grid-template-columns: repeat(2, 1fr); }
  .side { width: 165px; }
  .version-cards { grid-template-columns: 1fr 1fr; }
}

@media (max-width: 800px) {
  .wrap { flex-direction: column; }
  .side {
    width: 100%;
    height: auto;
    position: relative;
    top: 0;
    border-right: none;
    border-bottom: 1px solid var(--border);
    overflow-y: visible;
  }
  .card-grid, .lgrid { grid-template-columns: repeat(2, 1fr); }
  .version-cards { grid-template-columns: 1fr; }
  .hero { flex-direction: column; align-items: flex-start; gap: 10px; }
  .nav-search { width: 130px; }
}

@media (max-width: 500px) {
  .card-grid, .lgrid { grid-template-columns: 1fr; }
  .hero-stats { gap: 14px; }
  .stat-grid  { grid-template-columns: repeat(2, 1fr); }
  .nav-links  { display: none; }
  .nav-search { width: 100px; }
}

/* === PRINT ================================================================= */
@media print {
  .nav, .side, .dark-toggle, .skip-link { display: none !important; }
  .wrap  { display: block; }
  .main  { padding: 0; }
  body   { background: #fff; color: #000; font-size: 11pt; }
  a      { color: #000; }
  .card, .lcard, .section-box { break-inside: avoid; box-shadow: none; border: 1px solid #ccc; }
  .table th { background: #f0f0f0 !important; }
  .hero  { background: #f0f0f0 !important; color: #000 !important; border-radius: 0; }
}