/* ============================================================
   PPI GUIDEBOOK — MAIN DESIGN SYSTEM
   ============================================================ */

@import url('https://fonts.googleapis.com/css2?family=Syne:wght@400;500;600;700;800&family=DM+Sans:ital,opsz,wght@0,9..40,300;0,9..40,400;0,9..40,500;1,9..40,300&family=DM+Mono:wght@400;500&display=swap');

/* ── CSS Variables ─────────────────────────────────────────── */
:root {
  /* Core palette */
  --navy:        #080e1c;
  --navy-mid:    #0d1628;
  --navy-light:  #132040;
  --navy-card:   #111d35;
  --teal:        #00c9a7;
  --teal-dim:    #00a38a;
  --teal-glow:   rgba(0,201,167,0.15);
  --amber:       #f5a623;
  --amber-dim:   #c47f0e;
  --rose:        #ff6b8a;
  --lavender:    #a78bfa;

  /* Text */
  --text-primary:   #e8edf7;
  --text-secondary: #8fa3c8;
  --text-muted:     #4a6080;

  /* Borders */
  --border:       rgba(255,255,255,0.07);
  --border-teal:  rgba(0,201,167,0.25);

  /* Typography */
  --font-display: 'Syne', sans-serif;
  --font-body:    'DM Sans', sans-serif;
  --font-mono:    'DM Mono', monospace;

  /* Spacing */
  --section-pad: clamp(4rem, 8vw, 8rem);
  --content-max: 1200px;
  --content-narrow: 800px;

  /* Transitions */
  --ease: cubic-bezier(0.23, 1, 0.32, 1);
  --ease-spring: cubic-bezier(0.34, 1.56, 0.64, 1);

  /* Shadows */
  --shadow-card:  0 4px 32px rgba(0,0,0,0.4), 0 1px 0 rgba(255,255,255,0.05) inset;
  --shadow-glow:  0 0 40px rgba(0,201,167,0.2);
}

/* ── Reset & Base ──────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html {
  scroll-behavior: smooth;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
}

body {
  font-family: var(--font-body);
  background: var(--navy);
  color: var(--text-primary);
  line-height: 1.7;
  overflow-x: hidden;
}

/* Subtle grid texture */
body::before {
  content: '';
  position: fixed;
  inset: 0;
  background-image:
    linear-gradient(rgba(0,201,167,0.015) 1px, transparent 1px),
    linear-gradient(90deg, rgba(0,201,167,0.015) 1px, transparent 1px);
  background-size: 60px 60px;
  pointer-events: none;
  z-index: 0;
}

/* ── Typography ────────────────────────────────────────────── */
h1, h2, h3, h4, h5 {
  font-family: var(--font-display);
  line-height: 1.15;
  letter-spacing: -0.02em;
  color: var(--text-primary);
}

h1 { font-size: clamp(2.4rem, 5vw, 4rem); font-weight: 800; }
h2 { font-size: clamp(1.8rem, 3.5vw, 2.8rem); font-weight: 700; }
h3 { font-size: clamp(1.3rem, 2.5vw, 1.7rem); font-weight: 600; }
h4 { font-size: 1.15rem; font-weight: 600; }

p { color: var(--text-secondary); line-height: 1.8; }
p + p { margin-top: 1rem; }

a { color: var(--teal); text-decoration: none; transition: color 0.2s; }
a:hover { color: #fff; }

strong { color: var(--text-primary); font-weight: 500; }
em { color: var(--amber); font-style: normal; }

code {
  font-family: var(--font-mono);
  font-size: 0.85em;
  background: rgba(0,201,167,0.1);
  color: var(--teal);
  padding: 0.15em 0.45em;
  border-radius: 4px;
  border: 1px solid rgba(0,201,167,0.2);
}

/* ── Layout Utilities ──────────────────────────────────────── */
.container {
  max-width: var(--content-max);
  margin: 0 auto;
  padding: 0 clamp(1.5rem, 5vw, 3rem);
  position: relative;
  z-index: 1;
}

.container--narrow {
  max-width: var(--content-narrow);
  margin: 0 auto;
  padding: 0 clamp(1.5rem, 5vw, 3rem);
  position: relative;
  z-index: 1;
}

section { padding: var(--section-pad) 0; }

.grid-2 { display: grid; grid-template-columns: repeat(auto-fit, minmax(min(100%, 480px), 1fr)); gap: 2rem; }
.grid-3 { display: grid; grid-template-columns: repeat(auto-fit, minmax(min(100%, 320px), 1fr)); gap: 1.5rem; }
.grid-4 { display: grid; grid-template-columns: repeat(auto-fit, minmax(min(100%, 240px), 1fr)); gap: 1.5rem; }

/* ── Navigation ────────────────────────────────────────────── */
.nav {
  position: fixed;
  top: 0; left: 0; right: 0;
  z-index: 1000;
  padding: 1rem 0;
  transition: all 0.4s var(--ease);
}

.nav.scrolled {
  background: rgba(8,14,28,0.92);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border);
  padding: 0.7rem 0;
}

.nav__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  max-width: var(--content-max);
  margin: 0 auto;
  padding: 0 clamp(1.5rem, 5vw, 3rem);
}

.nav__logo {
  font-family: var(--font-display);
  font-weight: 800;
  font-size: 1.1rem;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 0.6rem;
  letter-spacing: -0.02em;
}

.nav__logo-dot {
  width: 8px; height: 8px;
  background: var(--teal);
  border-radius: 50%;
  box-shadow: 0 0 8px var(--teal);
  animation: pulse-dot 2s ease-in-out infinite;
}

@keyframes pulse-dot {
  0%, 100% { box-shadow: 0 0 8px var(--teal); transform: scale(1); }
  50% { box-shadow: 0 0 16px var(--teal), 0 0 30px rgba(0,201,167,0.4); transform: scale(1.2); }
}

.nav__links {
  display: flex;
  align-items: center;
  gap: 0.25rem;
  list-style: none;
}

.nav__links a {
  font-size: 0.85rem;
  font-weight: 500;
  color: var(--text-secondary);
  padding: 0.45rem 0.85rem;
  border-radius: 6px;
  transition: all 0.2s;
  white-space: nowrap;
}

.nav__links a:hover,
.nav__links a.active {
  color: var(--text-primary);
  background: rgba(255,255,255,0.06);
}

.nav__links a.active { color: var(--teal); }

.nav__cta {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--navy) !important;
  background: var(--teal) !important;
  padding: 0.5rem 1.2rem !important;
  border-radius: 6px !important;
}

.nav__cta:hover { background: #00e8c0 !important; transform: translateY(-1px); }

.nav__hamburger {
  display: none;
  flex-direction: column;
  gap: 5px;
  cursor: pointer;
  padding: 0.5rem;
  background: none;
  border: none;
}

.nav__hamburger span {
  display: block;
  width: 22px;
  height: 2px;
  background: var(--text-primary);
  border-radius: 2px;
  transition: all 0.3s;
}

/* ── Progress Bar ──────────────────────────────────────────── */
.progress-bar {
  position: fixed;
  top: 0; left: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--teal), var(--amber));
  z-index: 1001;
  transform-origin: left;
  transform: scaleX(0);
  transition: transform 0.1s linear;
  box-shadow: 0 0 8px rgba(0,201,167,0.6);
}

/* ── Cards ─────────────────────────────────────────────────── */
.card {
  background: var(--navy-card);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 2rem;
  box-shadow: var(--shadow-card);
  transition: transform 0.3s var(--ease), border-color 0.3s, box-shadow 0.3s;
  position: relative;
  overflow: hidden;
}

.card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 1px;
  background: linear-gradient(90deg, transparent, rgba(255,255,255,0.1), transparent);
}

.card:hover {
  transform: translateY(-4px);
  border-color: var(--border-teal);
  box-shadow: var(--shadow-card), 0 0 30px rgba(0,201,167,0.1);
}

.card--teal  { border-top: 2px solid var(--teal); }
.card--amber { border-top: 2px solid var(--amber); }
.card--rose  { border-top: 2px solid var(--rose); }
.card--lav   { border-top: 2px solid var(--lavender); }

/* ── Badges / Tags ─────────────────────────────────────────── */
.badge {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.72rem;
  font-weight: 600;
  font-family: var(--font-display);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  padding: 0.3rem 0.75rem;
  border-radius: 100px;
}

.badge--teal  { background: rgba(0,201,167,0.12); color: var(--teal); border: 1px solid rgba(0,201,167,0.25); }
.badge--amber { background: rgba(245,166,35,0.12); color: var(--amber); border: 1px solid rgba(245,166,35,0.25); }
.badge--rose  { background: rgba(255,107,138,0.12); color: var(--rose); border: 1px solid rgba(255,107,138,0.25); }
.badge--lav   { background: rgba(167,139,250,0.12); color: var(--lavender); border: 1px solid rgba(167,139,250,0.25); }

/* ── Buttons ───────────────────────────────────────────────── */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  font-family: var(--font-display);
  font-size: 0.9rem;
  font-weight: 600;
  padding: 0.85rem 2rem;
  border-radius: 8px;
  border: none;
  cursor: pointer;
  transition: all 0.25s var(--ease);
  text-decoration: none;
  white-space: nowrap;
}

.btn--primary {
  background: var(--teal);
  color: var(--navy);
}
.btn--primary:hover {
  background: #00e8c0;
  transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(0,201,167,0.35);
  color: var(--navy);
}

.btn--ghost {
  background: transparent;
  color: var(--text-primary);
  border: 1px solid var(--border);
}
.btn--ghost:hover {
  border-color: var(--teal);
  color: var(--teal);
  background: var(--teal-glow);
  transform: translateY(-2px);
}

.btn--amber {
  background: var(--amber);
  color: var(--navy);
}
.btn--amber:hover {
  background: #ffb83d;
  transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(245,166,35,0.35);
  color: var(--navy);
}

/* ── Section Headers ───────────────────────────────────────── */
.section-header {
  margin-bottom: clamp(2.5rem, 5vw, 4rem);
}

.section-header--center { text-align: center; }

.section-label {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  letter-spacing: 0.15em;
  text-transform: uppercase;
  color: var(--teal);
  margin-bottom: 0.75rem;
}

.section-header h2 { margin-bottom: 1rem; }
.section-header p  { max-width: 580px; font-size: 1.05rem; }
.section-header--center p { margin: 0 auto; }

/* ── Dividers ──────────────────────────────────────────────── */
.divider {
  height: 1px;
  background: linear-gradient(90deg, transparent, var(--border), transparent);
  margin: 0;
}

/* ── Tooltip ───────────────────────────────────────────────── */
.tooltip-wrap { position: relative; display: inline; }

.tooltip-term {
  color: var(--teal);
  border-bottom: 1px dashed var(--teal);
  cursor: help;
}

.tooltip-box {
  display: none;
  position: absolute;
  bottom: calc(100% + 8px);
  left: 50%;
  transform: translateX(-50%);
  background: var(--navy-mid);
  border: 1px solid var(--border-teal);
  border-radius: 10px;
  padding: 0.85rem 1rem;
  width: 260px;
  font-size: 0.83rem;
  line-height: 1.5;
  color: var(--text-secondary);
  z-index: 100;
  box-shadow: 0 8px 32px rgba(0,0,0,0.5);
  pointer-events: none;
}

.tooltip-box::after {
  content: '';
  position: absolute;
  top: 100%; left: 50%;
  transform: translateX(-50%);
  border: 6px solid transparent;
  border-top-color: var(--navy-mid);
}

.tooltip-wrap:hover .tooltip-box { display: block; animation: tooltip-in 0.15s var(--ease); }

@keyframes tooltip-in {
  from { opacity: 0; transform: translateX(-50%) translateY(4px); }
  to   { opacity: 1; transform: translateX(-50%) translateY(0); }
}

/* ── Accordion ─────────────────────────────────────────────── */
.accordion { border: 1px solid var(--border); border-radius: 12px; overflow: hidden; }

.accordion__item { border-bottom: 1px solid var(--border); }
.accordion__item:last-child { border-bottom: none; }

.accordion__trigger {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1.25rem 1.5rem;
  background: none;
  border: none;
  cursor: pointer;
  color: var(--text-primary);
  font-family: var(--font-display);
  font-size: 1rem;
  font-weight: 600;
  text-align: left;
  transition: background 0.2s;
  gap: 1rem;
}

.accordion__trigger:hover { background: rgba(255,255,255,0.03); }

.accordion__icon {
  width: 20px; height: 20px;
  flex-shrink: 0;
  color: var(--teal);
  transition: transform 0.3s var(--ease);
}

.accordion__trigger[aria-expanded="true"] .accordion__icon { transform: rotate(45deg); }

.accordion__body {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.4s var(--ease);
}

.accordion__body-inner { padding: 0 1.5rem 1.5rem; }

/* ── Callout Boxes ─────────────────────────────────────────── */
.callout {
  border-radius: 12px;
  padding: 1.25rem 1.5rem;
  border-left: 3px solid;
  display: flex;
  gap: 1rem;
  align-items: flex-start;
}

.callout--info    { background: rgba(0,201,167,0.07); border-color: var(--teal); }
.callout--warn    { background: rgba(245,166,35,0.07); border-color: var(--amber); }
.callout--key     { background: rgba(167,139,250,0.07); border-color: var(--lavender); }
.callout--example { background: rgba(255,107,138,0.07); border-color: var(--rose); }

.callout__icon { font-size: 1.2rem; flex-shrink: 0; margin-top: 0.1rem; }
.callout__title { font-weight: 600; color: var(--text-primary); margin-bottom: 0.25rem; font-size: 0.9rem; font-family: var(--font-display); }
.callout p { margin: 0; font-size: 0.9rem; }

/* ── Footer ────────────────────────────────────────────────── */
.footer {
  border-top: 1px solid var(--border);
  padding: 3rem 0;
  margin-top: auto;
}

.footer__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 2rem;
  flex-wrap: wrap;
}

.footer__copy {
  font-size: 0.82rem;
  color: var(--text-muted);
}

.footer__links {
  display: flex;
  gap: 1.5rem;
  list-style: none;
}

.footer__links a {
  font-size: 0.82rem;
  color: var(--text-muted);
  transition: color 0.2s;
}

.footer__links a:hover { color: var(--teal); }

/* ── Scroll Reveal ─────────────────────────────────────────── */
.reveal {
  opacity: 0;
  transform: translateY(28px);
  transition: opacity 0.7s var(--ease), transform 0.7s var(--ease);
}

.reveal.visible {
  opacity: 1;
  transform: translateY(0);
}

.reveal--delay-1 { transition-delay: 0.1s; }
.reveal--delay-2 { transition-delay: 0.2s; }
.reveal--delay-3 { transition-delay: 0.3s; }
.reveal--delay-4 { transition-delay: 0.4s; }

/* ── Responsive ────────────────────────────────────────────── */
@media (max-width: 768px) {
  .nav__links { display: none; }
  .nav__links.open {
    display: flex;
    flex-direction: column;
    position: absolute;
    top: 100%; left: 0; right: 0;
    background: rgba(8,14,28,0.97);
    backdrop-filter: blur(20px);
    padding: 1rem;
    border-bottom: 1px solid var(--border);
    gap: 0.25rem;
  }
  .nav__hamburger { display: flex; }
  .grid-2, .grid-3, .grid-4 { grid-template-columns: 1fr; }
}

/* ── Chapter page shared styles ─────────────────────────────── */
.page-hero {
  padding: clamp(7rem, 12vw, 10rem) 0 clamp(3rem, 6vw, 5rem);
  position: relative;
  overflow: hidden;
}

.page-hero__eyebrow {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 1.25rem;
}

.page-hero__chapter {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--text-muted);
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.page-hero p {
  font-size: clamp(1rem, 2vw, 1.2rem);
  max-width: 680px;
  margin-top: 1.25rem;
}

/* ── Sticky sidebar TOC ─────────────────────────────────────── */
.toc {
  position: sticky;
  top: 6rem;
  align-self: start;
  padding: 1.5rem;
  background: var(--navy-card);
  border: 1px solid var(--border);
  border-radius: 12px;
}

.toc__title {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: 1rem;
}

.toc__list { list-style: none; }
.toc__list li + li { margin-top: 0.25rem; }

.toc__list a {
  font-size: 0.85rem;
  color: var(--text-secondary);
  padding: 0.3rem 0.6rem;
  border-radius: 6px;
  display: block;
  transition: all 0.2s;
  border-left: 2px solid transparent;
}

.toc__list a:hover,
.toc__list a.active {
  color: var(--teal);
  border-left-color: var(--teal);
  background: var(--teal-glow);
}

/* ── Table styles ───────────────────────────────────────────── */
.table-wrap { overflow-x: auto; border-radius: 12px; border: 1px solid var(--border); }

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.9rem;
}

thead {
  background: var(--navy-light);
}

th {
  padding: 0.9rem 1.25rem;
  text-align: left;
  font-family: var(--font-display);
  font-size: 0.8rem;
  font-weight: 600;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  color: var(--text-secondary);
  white-space: nowrap;
}

td {
  padding: 0.9rem 1.25rem;
  border-top: 1px solid var(--border);
  color: var(--text-secondary);
  vertical-align: top;
}

tr:hover td { background: rgba(255,255,255,0.02); }

/* Highlight cells */
.td-teal  { color: var(--teal); font-weight: 500; }
.td-amber { color: var(--amber); font-weight: 500; }

/* ── Step list ──────────────────────────────────────────────── */
.step-list { list-style: none; counter-reset: steps; display: flex; flex-direction: column; gap: 1.5rem; }

.step-list li {
  counter-increment: steps;
  display: flex;
  gap: 1.25rem;
  align-items: flex-start;
}

.step-list li::before {
  content: counter(steps);
  display: flex;
  align-items: center;
  justify-content: center;
  min-width: 32px;
  height: 32px;
  border-radius: 50%;
  background: var(--teal-glow);
  border: 1px solid var(--border-teal);
  color: var(--teal);
  font-family: var(--font-display);
  font-size: 0.8rem;
  font-weight: 700;
  flex-shrink: 0;
  margin-top: 0.15rem;
}

/* ── Reading layout: content + sidebar ──────────────────────── */
.reading-layout {
  display: grid;
  grid-template-columns: 1fr 240px;
  gap: 4rem;
  align-items: start;
}

@media (max-width: 960px) {
  .reading-layout {
    grid-template-columns: 1fr;
  }
  .toc { position: static; display: none; }
}

/* ── Annotation / figure caption ───────────────────────────── */
.fig-caption {
  font-size: 0.82rem;
  color: var(--text-muted);
  text-align: center;
  margin-top: 0.75rem;
  font-style: italic;
}

/* ── Pull quote ─────────────────────────────────────────────── */
.pull-quote {
  border-left: 3px solid var(--teal);
  padding: 1rem 1.5rem;
  margin: 2rem 0;
  background: var(--teal-glow);
  border-radius: 0 8px 8px 0;
}

.pull-quote p {
  font-size: 1.1rem;
  font-style: italic;
  color: var(--text-primary);
  line-height: 1.6;
}

/* ── Inline highlight ───────────────────────────────────────── */
.highlight { color: var(--teal); }
.highlight--amber { color: var(--amber); }
.highlight--rose  { color: var(--rose); }
.highlight--lav   { color: var(--lavender); }