/* =====================================================================
   Phasor — shared chapter stylesheet
   Used by every file in public/chapters/*.html
   Palette: Oxford Navy #0F1F47 · Princeton Orange #F9A033
            Chalk White #F7FAFC · BOSE Yellow #FCB908 · BOSE Purple #15002B
   ===================================================================== */

:root {
  --bg: #F7FAFC;
  --bg2: #EEF1F6;
  --surface: #FFFFFF;
  --surface2: #F2F5FA;

  --border: #D5DCE5;
  --border-soft: #E4E9F0;

  --text: #0F1F47;
  --text-2: #3A4C70;
  --text-3: #8A93A6;

  --accent: #0F1F47;
  --accent-2: #F9A033;
  --accent-3: #15002B;

  --accent-soft: rgba(15, 31, 71, 0.08);
  --accent-2-soft: rgba(249, 160, 51, 0.10);
  --accent-3-soft: rgba(21, 0, 43, 0.08);

  --highlight: #EEF3FF;
  --mark: #FFF6E5;

  --radius: 6px;
  --shadow: 0 2px 16px rgba(15, 31, 71, 0.10);
}

/* --------------------------- Reset / base --------------------------- */

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

html { scroll-behavior: smooth; }

body {
  background: var(--bg);
  color: var(--text);
  font-family: 'Poppins', system-ui, sans-serif;
  font-size: clamp(15px, 1.7vw, 16.5px);
  line-height: 1.9;
}

/* --------------------------- Header --------------------------- */

header {
  background: linear-gradient(150deg, #07122a 0%, #102347 50%, #0F1F47 100%);
  color: var(--bg);
  padding: clamp(36px, 6vw, 64px) clamp(24px, 6vw, 80px) clamp(32px, 5vw, 56px);
  position: relative;
  overflow: hidden;
}

header::before {
  content: "";
  position: absolute; inset: 0;
  background:
    radial-gradient(ellipse at 15% 70%, rgba(249, 160, 51, 0.14) 0%, transparent 55%),
    radial-gradient(ellipse at 85% 20%, rgba(252, 185, 8, 0.08) 0%, transparent 50%);
  pointer-events: none;
}

header::after {
  content: "";
  position: absolute; bottom: 0; left: 0; right: 0;
  height: 4px;
  background: linear-gradient(90deg, var(--accent-2) 0%, #FCB908 100%);
  opacity: 0.9;
}

.header-inner { max-width: 840px; margin: 0 auto; position: relative; }

.eyebrow {
  font-size: 0.70rem; font-weight: 700;
  letter-spacing: 0.18em; text-transform: uppercase;
  color: var(--accent-2);
  margin-bottom: 10px;
}

header h1 {
  font-family: 'Times New Roman', Times, serif;
  font-size: clamp(2.2rem, 5.5vw, 3.4rem);
  font-weight: 600;
  color: var(--bg);
  line-height: 1.15;
  letter-spacing: -0.01em;
}

.header-sub {
  margin-top: 10px;
  font-size: 0.94rem;
  color: rgba(247, 250, 252, 0.75);
  font-style: italic;
  max-width: 600px;
}

/* --------------------------- Layout --------------------------- */

.page-wrap {
  display: flex;
  align-items: flex-start;
  max-width: 1140px;
  margin: 0 auto;
  padding: 0 clamp(14px, 4vw, 36px);
  gap: 36px;
}

main {
  flex: 1;
  min-width: 0;
  padding: clamp(28px, 4vw, 48px) 0 100px;
}

/* --------------------------- Sidebar TOC --------------------------- */

.sidebar {
  position: sticky;
  top: 28px;
  width: 210px;
  flex-shrink: 0;
  padding: 24px 0;
  display: none;
  max-height: 95vh;
  overflow-y: auto;
}

@media (min-width: 920px) { .sidebar { display: block; } }

.nav-label {
  font-size: 0.66rem; font-weight: 700;
  letter-spacing: 0.14em; text-transform: uppercase;
  color: var(--text-3);
  padding: 0 10px;
  margin-bottom: 8px;
}

.sidebar nav a {
  display: block;
  font-size: 0.80rem;
  color: var(--text-2);
  text-decoration: none;
  padding: 4px 10px;
  border-radius: 4px;
  border-left: 2px solid transparent;
  transition: background 0.15s, border-color 0.15s, color 0.15s;
  line-height: 1.5;
}

.sidebar nav a:hover,
.sidebar nav a.active {
  background: var(--bg2);
  border-left-color: var(--accent-2);
  color: var(--accent);
}

/* --------------------------- Mobile nav --------------------------- */

.nav-toggle {
  position: fixed;
  bottom: 22px; right: 22px;
  width: 44px; height: 44px;
  background: var(--accent-2);
  color: var(--accent);
  border: none;
  border-radius: 50%;
  font-size: 1.2rem;
  cursor: pointer;
  box-shadow: 0 4px 16px rgba(15, 31, 71, 0.35);
  z-index: 500;
  display: flex; align-items: center; justify-content: center;
}

@media (min-width: 920px) { .nav-toggle { display: none; } }

.mobile-nav {
  display: none;
  position: fixed;
  bottom: 76px; right: 14px;
  width: 240px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  z-index: 500;
  padding: 10px 0;
  max-height: 72vh;
  overflow-y: auto;
}

.mobile-nav.open { display: block; }

.mobile-nav a {
  display: block;
  font-size: 0.81rem;
  color: var(--text-2);
  text-decoration: none;
  padding: 5px 14px;
}

.mobile-nav a:hover { background: var(--bg2); color: var(--accent-2); }

/* --------------------------- Typography --------------------------- */

.section { margin-top: 60px; }
.section:first-child { margin-top: 0; }
.subsection { margin-top: 44px; }

h2 {
  font-family: 'Times New Roman', Times, serif;
  font-size: clamp(1.35rem, 2.8vw, 1.65rem);
  font-weight: 600;
  color: var(--accent);
  border-bottom: 1.5px solid var(--border);
  padding-bottom: 8px;
  margin-bottom: 20px;
  scroll-margin-top: 32px;
}

h3 {
  font-family: 'Times New Roman', Times, serif;
  font-size: clamp(1.08rem, 2.2vw, 1.27rem);
  font-weight: 600;
  color: var(--text);
  margin: 0 0 12px;
  scroll-margin-top: 32px;
}

h4 {
  font-family: 'Poppins', sans-serif;
  font-size: 0.82rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-3);
  margin: 22px 0 8px;
}

p { color: var(--text); margin-bottom: 14px; }
ul, ol { padding-left: 24px; margin: 8px 0 14px; }
li { margin-bottom: 6px; }
hr { border: none; border-top: 1px solid var(--border-soft); margin: 48px 0; }
strong { font-weight: 700; color: var(--text); }
em { font-style: italic; }

/* --------------------------- Math blocks --------------------------- */

.math-block {
  background: var(--surface);
  border: 1px solid var(--border-soft);
  border-radius: var(--radius);
  padding: 14px 22px;
  margin: 14px 0;
  overflow-x: auto;
  text-align: center;
}

.math-block.key {
  background: linear-gradient(135deg, var(--highlight), #E8EEFF);
  border: 1.5px solid var(--accent-2);
  box-shadow: 0 0 0 3px rgba(249, 160, 51, 0.10);
}

.math-block .mlabel {
  font-size: 0.72rem; font-weight: 700;
  letter-spacing: 0.10em; text-transform: uppercase;
  color: var(--accent-2);
  display: block;
  margin-bottom: 6px;
  text-align: left;
}

.key-formula {
  background: linear-gradient(135deg, var(--highlight), #E8EEFF);
  border: 1.5px solid var(--accent-2);
  border-radius: var(--radius);
  padding: 12px 20px;
  margin: 14px 0;
  text-align: center;
  box-shadow: 0 0 0 3px rgba(249, 160, 51, 0.10);
}

.key-formula .kf-label {
  font-size: 0.70rem; font-weight: 700;
  letter-spacing: 0.10em; text-transform: uppercase;
  color: var(--accent-2);
  display: block;
  margin-bottom: 6px;
  text-align: left;
}

/* --------------------------- Callouts --------------------------- */

.intro-box {
  background: var(--surface);
  border: 1px solid var(--border);
  border-left: 4px solid var(--accent-2);
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 18px 22px;
  margin-bottom: 32px;
  font-size: 1rem;
  color: var(--text-2);
}

.definition {
  background: var(--surface);
  border: 1px solid var(--border-soft);
  border-left: 3px solid var(--accent);
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 14px 18px;
  margin: 16px 0;
}

.definition .def-label {
  font-size: 0.68rem; font-weight: 700;
  letter-spacing: 0.12em; text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 4px;
}

.definition p { margin-bottom: 0; }
.definition p + p { margin-top: 10px; }

.note {
  border-left: 3px solid var(--accent-3);
  background: linear-gradient(90deg, var(--accent-3-soft), var(--surface));
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 11px 16px;
  margin: 14px 0;
  font-size: 0.95rem;
  color: var(--text-2);
}

.note .note-label {
  font-size: 0.67rem; font-weight: 700;
  letter-spacing: 0.10em; text-transform: uppercase;
  color: var(--accent-3);
  margin-bottom: 4px;
}

.note p { margin-bottom: 6px; }

.tip {
  border-left: 3px solid var(--accent-2);
  background: linear-gradient(90deg, var(--accent-2-soft), var(--surface));
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 11px 16px;
  margin: 14px 0;
  font-size: 0.95rem;
  color: var(--text-2);
}

.tip .tip-label {
  font-size: 0.67rem; font-weight: 700;
  letter-spacing: 0.10em; text-transform: uppercase;
  color: var(--accent-2);
  margin-bottom: 4px;
}

.shortcut {
  border-left: 3px solid #7a4fa0;
  background: linear-gradient(90deg, rgba(122, 79, 160, 0.10), var(--surface));
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 12px 16px;
  margin: 16px 0;
  font-size: 0.95rem;
  color: var(--text-2);
}

.shortcut .sc-label {
  font-size: 0.67rem; font-weight: 700;
  letter-spacing: 0.10em; text-transform: uppercase;
  color: #7a4fa0;
  margin-bottom: 4px;
}

/* --------------------------- Grids, tables, results --------------------------- */

.formula-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin: 16px 0;
}

@media (max-width: 600px) { .formula-grid { grid-template-columns: 1fr; } }

.formula-cell {
  background: var(--surface);
  border: 1px solid var(--border-soft);
  border-radius: var(--radius);
  padding: 12px 16px;
}

.formula-cell .fc-label {
  font-size: 0.70rem; font-weight: 700;
  letter-spacing: 0.10em; text-transform: uppercase;
  color: var(--accent-2);
  margin-bottom: 6px;
}

.formula-cell p { margin-bottom: 8px; }

.imp-table {
  width: 100%;
  border-collapse: collapse;
  margin: 16px 0;
  font-size: 0.93rem;
}

.imp-table th {
  background: var(--bg2);
  font-size: 0.74rem; font-weight: 700;
  letter-spacing: 0.08em; text-transform: uppercase;
  color: var(--text-2);
  padding: 9px 14px;
  text-align: left;
  border-bottom: 2px solid var(--border);
}

.imp-table td {
  padding: 9px 14px;
  border-bottom: 1px solid var(--border-soft);
  vertical-align: middle;
}

.imp-table tr:last-child td { border-bottom: none; }
.imp-table tr:hover td { background: var(--bg2); }

.result-box {
  background: linear-gradient(135deg, var(--highlight) 0%, #E4EAFF 100%);
  border: 1.5px solid #B0C4F0;
  border-radius: var(--radius);
  padding: 18px 22px;
  margin: 18px 0;
}

.result-box .result-label {
  font-size: 0.68rem; font-weight: 700;
  letter-spacing: 0.12em; text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 8px;
}

/* --------------------------- Collapsibles --------------------------- */

.expand-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--accent-2);
  background: var(--accent-2-soft);
  border: 1px solid rgba(249, 160, 51, 0.3);
  border-radius: 4px;
  padding: 4px 10px;
  cursor: pointer;
  user-select: none;
  transition: background 0.15s;
}

.expand-btn:hover { background: rgba(249, 160, 51, 0.18); }

.expand-btn .arr {
  font-size: 0.7rem;
  transition: transform 0.2s;
  display: inline-block;
}

.expand-btn.open .arr { transform: rotate(90deg); }

.collapse-block {
  display: none;
  margin-top: 10px;
  padding: 14px 18px;
  background: var(--surface);
  border: 1px solid var(--border-soft);
  border-left: 3px solid var(--accent-2);
  border-radius: 0 var(--radius) var(--radius) 0;
}

.collapse-block.open { display: block; }
.collapse-block > p:first-child { margin-top: 0; }
.collapse-block > p:last-child { margin-bottom: 0; }

/* --------------------------- Scrollbar --------------------------- */

::-webkit-scrollbar { width: 5px; height: 5px; }
::-webkit-scrollbar-track { background: var(--bg); }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 3px; }
/* =========================================================
   MARK COMPLETE BUTTON
   ========================================================= */
.mark-complete-wrap {
  margin-top: 60px;
  padding-top: 40px;
  border-top: 1px solid var(--border-soft);
  display: flex;
  justify-content: center;
}

.mark-complete-btn {
  padding: 14px 32px;
  font-family: 'Poppins', sans-serif;
  font-size: 0.95rem;
  font-weight: 600;
  letter-spacing: 0.04em;
  color: var(--bg);
  background: var(--accent-2);
  border: 1.5px solid var(--accent-2);
  border-radius: 8px;
  cursor: pointer;
  transition: background 0.15s, transform 0.1s, opacity 0.15s;
}

.mark-complete-btn:hover:not(:disabled) {
  background: #e88f1f;
  transform: translateY(-1px);
}

.mark-complete-btn:active:not(:disabled) {
  transform: translateY(0);
}

.mark-complete-btn:disabled {
  opacity: 0.7;
  cursor: not-allowed;
}

.mark-complete-btn.completed {
  background: transparent;
  color: var(--accent-2);
  border-color: var(--accent-2);
  cursor: default;
}