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

:root {
  --bg:        #fdfcfa;
  --bg-warm:   #f7f4ef;
  --bg-eq:     #f2ede4;
  --fg:        #1a1814;
  --fg2:       #3d3828;
  --muted:     #7a7060;
  --border:    #ddd8ce;
  --border-hv: #c8c0b0;
  --accent:    #4a4030;
  --nav-bg:    #1a1814;
  --nav-text:  #f0ebe0;
  --nav-muted: rgba(240,235,224,0.38);
  --nav-line:  #b8a880;
  --code-bg:   #1c1a14;
  --code-txt:  #d8d0c0;
  --pos:       #2a5e35;
  --neg:       #7a2010;
}

html { scroll-behavior: smooth; }

body {
  background: var(--bg);
  color: var(--fg);
  font-family: 'EB Garamond', Georgia, serif;
  font-size: 19px;
  line-height: 1.85;
}

/* NAV */
.nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--nav-bg);
  display: flex;
  align-items: stretch;
  border-bottom: 2px solid var(--nav-line);
}
.nav-brand {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 2.5px;
  text-transform: uppercase;
  color: var(--nav-text);
  padding: 12px 20px;
  border-right: 0.5px solid rgba(255,255,255,0.07);
  white-space: nowrap;
}
.nav a {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 10px;
  font-weight: 700;
  letter-spacing: 2px;
  text-transform: uppercase;
  color: var(--nav-muted);
  text-decoration: none;
  padding: 12px 16px;
  border-bottom: 2px solid transparent;
  margin-bottom: -2px;
  transition: color 0.15s, border-color 0.15s;
  white-space: nowrap;
}
.nav a:hover { color: var(--nav-text); }
.nav a.active { color: var(--nav-text); border-bottom-color: var(--nav-line); }

/* SECTIONS */
.part { display: none; max-width: 800px; margin: 0 auto; padding: 64px 36px 110px; }
.part.active { display: block; }

/* HEADER */
.art-header { border-bottom: 1px solid var(--border); padding-bottom: 36px; margin-bottom: 56px; }
.part-label {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 9px;
  font-weight: 700;
  letter-spacing: 4px;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 14px;
}
.art-header h1 {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: clamp(24px, 3.5vw, 38px);
  font-weight: 700;
  line-height: 1.15;
  color: var(--fg);
  margin-bottom: 18px;
}
.art-header .sub {
  font-size: 16px;
  font-style: italic;
  color: var(--muted);
  line-height: 1.65;
  max-width: 580px;
}

/* HEADINGS */
h2 {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 3px;
  text-transform: uppercase;
  color: var(--muted);
  margin-top: 56px;
  margin-bottom: 18px;
  padding-top: 36px;
  border-top: 0.5px solid var(--border);
}
h2 .sn { color: var(--accent); margin-right: 10px; }

h3 {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 14px;
  font-weight: 700;
  color: var(--fg);
  margin-top: 34px;
  margin-bottom: 12px;
  letter-spacing: 0.3px;
}

p { margin-bottom: 20px; color: var(--fg2); }

.dropcap::first-letter {
  font-size: 60px;
  font-weight: 700;
  float: left;
  line-height: 0.82;
  margin: 8px 10px -4px 0;
  color: var(--accent);
  font-family: 'EB Garamond', Georgia, serif;
}

/* MATH */
.eq-wrap {
  background: var(--bg-eq);
  border-left: 2px solid var(--border-hv);
  padding: 16px 22px;
  margin: 24px 0;
  overflow-x: auto;
}
.eq-label {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 8px;
  font-weight: 700;
  letter-spacing: 2.5px;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 8px;
  display: block;
}
.eq-note { font-size: 14px; font-style: italic; color: var(--muted); margin: -14px 0 20px 4px; }

/* TABLE */
table { width: 100%; border-collapse: collapse; margin: 22px 0; font-size: 15.5px; }
thead th {
  background: var(--fg);
  color: #f0ebe0;
  padding: 9px 14px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 9px;
  font-weight: 700;
  letter-spacing: 1.5px;
  text-transform: uppercase;
  text-align: center;
}
thead th:first-child { text-align: left; }
tbody td { padding: 9px 14px; border-bottom: 0.5px solid var(--border); text-align: center; color: var(--fg2); }
tbody td:first-child { text-align: left; font-style: italic; color: var(--muted); font-size: 15px; }
tbody tr:nth-child(even) { background: var(--bg-warm); }
.upos { color: var(--pos); font-weight: 700; font-family: 'JetBrains Mono', monospace; font-size: 14px; }
.uneg { color: var(--neg); font-weight: 700; font-family: 'JetBrains Mono', monospace; font-size: 14px; }
.uneu { color: var(--muted); font-family: 'JetBrains Mono', monospace; font-size: 14px; }

/* CALLOUT */
.callout {
  background: var(--bg-warm);
  border: 0.5px solid var(--border);
  padding: 18px 22px;
  margin: 22px 0;
  font-size: 16px;
}
.callout-label {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 8px;
  font-weight: 700;
  letter-spacing: 2.5px;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 9px;
}
.callout p { font-size: 15px; color: var(--fg2); margin: 0; line-height: 1.7; }

/* DEFINITION */
.defn {
  border-left: 2px solid var(--border-hv);
  padding: 14px 18px;
  margin: 20px 0;
  background: var(--bg-warm);
}
.defn-label {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 8px;
  font-weight: 700;
  letter-spacing: 2.5px;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 8px;
}
.defn p { font-size: 15px; color: var(--fg2); margin: 0; line-height: 1.7; }

/* PROOF */
.proof { border: 0.5px solid var(--border); padding: 16px 20px; margin: 22px 0; }
.proof-label {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 8px;
  font-weight: 700;
  letter-spacing: 2.5px;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 10px;
}
.proof p { font-size: 15px; color: var(--fg2); margin-bottom: 6px; }

/* THRESHOLD BAR */
.thresh { margin: 22px 0; }
.thresh-bar { display: flex; height: 36px; overflow: hidden; border-radius: 2px; }
.seg { display: flex; align-items: center; justify-content: center; flex: 1; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 10px; font-weight: 700; letter-spacing: 1px; }
.seg-r { background: #c8b8a8; color: #3a2a1a; }
.seg-b { background: #a89878; color: #f0e8d8; }
.seg-a { background: #5a7858; color: #e8f0e4; }
.thresh-axis { display: flex; justify-content: space-between; margin-top: 6px; font-family: 'JetBrains Mono', monospace; font-size: 10px; color: var(--muted); }

/* DECISION BOX */
.dbox {
  background: var(--fg);
  color: #f0ebe0;
  padding: 26px 30px;
  margin: 36px 0;
  text-align: center;
}
.dbox-label {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 8px;
  font-weight: 700;
  letter-spacing: 3px;
  text-transform: uppercase;
  color: rgba(240,235,224,0.4);
  margin-bottom: 12px;
}
.dbox-rule { font-size: 17px; color: #d4c090; font-family: 'EB Garamond', Georgia, serif; line-height: 1.9; }

/* CODE */
.code-label {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 8px;
  font-weight: 700;
  letter-spacing: 2.5px;
  text-transform: uppercase;
  color: var(--muted);
  margin-top: 32px;
  margin-bottom: -6px;
}
pre.code {
  background: var(--code-bg);
  color: var(--code-txt);
  padding: 24px 28px;
  overflow-x: auto;
  font-family: 'JetBrains Mono', monospace;
  font-size: 12.5px;
  line-height: 1.72;
  margin: 8px 0 28px;
  border: 0.5px solid rgba(255,255,255,0.04);
}
.kw  { color: #c8886a; }
.fn  { color: #88b8d8; }
.st  { color: #90c070; }
.nu  { color: #d0b860; }
.cm  { color: #5e7058; font-style: italic; }

/* LISTS */
ol.steps { padding-left: 24px; margin: 16px 0; }
ol.steps li { margin-bottom: 9px; color: var(--fg2); font-size: 17px; }
ul.bul { padding-left: 24px; margin: 14px 0; }
ul.bul li { margin-bottom: 8px; color: var(--fg2); font-size: 17px; }

/* SIGNAL TABLE */
.sig-tbl td:first-child { font-style: normal; font-family: 'JetBrains Mono', monospace; font-size: 12px; }

/* PART FOOTER */
.part-footer { margin-top: 72px; padding-top: 28px; border-top: 0.5px solid var(--border); display: flex; justify-content: flex-end; }
.next-btn {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 10px;
  font-weight: 700;
  letter-spacing: 2px;
  text-transform: uppercase;
  background: var(--fg);
  color: #f0ebe0;
  border: none;
  padding: 11px 22px;
  cursor: pointer;
  transition: background 0.15s;
}
.next-btn:hover { background: #3a3020; }

/* FOOTNOTES */
.footnotes { margin-top: 56px; padding-top: 24px; border-top: 0.5px solid var(--border); }
.footnotes p { font-size: 14px; color: var(--muted); margin-bottom: 9px; line-height: 1.65; }

.surface-fig { margin: 28px 0 32px; }
.surface-caption {
  font-family: 'EB Garamond', Georgia, serif;
  font-size: 14px;
  font-style: italic;
  color: var(--muted);
  margin-top: 10px;
  line-height: 1.6;
  padding: 0 4px;
}
.surface-caption-label {
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-style: normal;
  font-size: 10px;
  font-weight: 700;
  letter-spacing: 2px;
  text-transform: uppercase;
  color: var(--accent);
  margin-right: 8px;
}