:root {
  --accent: #003087;
  --accent-dark: #00226b;
  --accent-light: #e8edf7;
  --teal: #087f8c;
  --green: #12805c;
  --amber: #a16207;
  --purple: #6d4aff;
  --text: #1a1a1a;
  --text-muted: #666;
  --border: #e2e5ea;
  --bg: #fff;
  --bg-alt: #f6f7fb;
  --radius: 8px;
  --max-w: 1100px;
  --font: system-ui, -apple-system, "Segoe UI", Arial, "PingFang SC",
    "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
}

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

html {
  scroll-behavior: smooth;
}

body {
  min-width: 320px;
  color: var(--text);
  background: var(--bg);
  font-family: var(--font);
  font-size: 15px;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

a {
  color: inherit;
}

.container {
  width: 100%;
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 0 28px;
}

.skip-link {
  position: fixed;
  top: 10px;
  left: 12px;
  z-index: 1000;
  padding: 8px 12px;
  border-radius: 6px;
  background: var(--accent);
  color: #fff;
  font-weight: 700;
  text-decoration: none;
  transform: translateY(-150%);
  transition: transform 0.2s ease;
}

.skip-link:focus {
  transform: translateY(0);
}

:focus-visible {
  outline: 3px solid rgba(109, 74, 255, 0.45);
  outline-offset: 3px;
}

/* Navigation */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  padding: 13px 0;
  border-bottom: 1px solid var(--border);
  background: rgba(255, 255, 255, 0.96);
  backdrop-filter: blur(10px);
}

.nav-inner {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
}

.nav-logo {
  color: var(--accent);
  font-size: 16px;
  font-weight: 700;
  letter-spacing: 0.01em;
  text-decoration: none;
}

.nav-links {
  display: flex;
  flex: 1;
  min-width: 0;
  justify-content: flex-end;
  gap: 24px;
}

.nav-links a {
  color: var(--text-muted);
  font-size: 14px;
  text-decoration: none;
  white-space: nowrap;
  transition: color 0.2s ease;
}

.nav-links a:hover {
  color: var(--accent);
}

.language-toggle {
  display: inline-flex;
  flex-shrink: 0;
  min-width: 72px;
  height: 30px;
  align-items: center;
  justify-content: center;
  padding: 0 12px;
  border: 1px solid var(--border);
  border-radius: 999px;
  background: #fff;
  color: var(--accent);
  cursor: pointer;
  font: 600 13px/1 var(--font);
  transition: border-color 0.2s ease, background-color 0.2s ease;
}

.language-toggle:hover {
  border-color: rgba(0, 48, 135, 0.35);
  background: var(--accent-light);
}

.nav-toggle {
  display: none;
  width: 32px;
  height: 30px;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: #fff;
  cursor: pointer;
}

.nav-toggle-lines,
.nav-toggle-lines::before,
.nav-toggle-lines::after {
  position: relative;
  display: block;
  width: 15px;
  height: 2px;
  border-radius: 999px;
  background: var(--accent);
}

.nav-toggle-lines::before,
.nav-toggle-lines::after {
  position: absolute;
  left: 0;
  content: "";
}

.nav-toggle-lines::before {
  top: -5px;
}

.nav-toggle-lines::after {
  top: 5px;
}

/* Hero */
.pi-hero {
  padding: 46px 0 42px;
  border-bottom: 1px solid var(--border);
  background: #fff;
}

.pi-hero-grid {
  display: grid;
  grid-template-columns: minmax(0, 1.25fr) minmax(350px, 0.75fr);
  align-items: center;
  gap: clamp(36px, 5vw, 68px);
}

.pi-hero-copy {
  min-width: 0;
}

.pi-eyebrow,
.section-kicker {
  margin-bottom: 7px;
  color: var(--teal);
  font-size: 12px;
  font-weight: 800;
  letter-spacing: 0.09em;
  text-transform: uppercase;
}

.pi-hero-title {
  margin-bottom: 15px;
  color: var(--accent);
  font-size: clamp(34px, 5vw, 54px);
  font-weight: 800;
  letter-spacing: -0.035em;
  line-height: 1.08;
  text-wrap: balance;
}

.pi-hero-lead {
  max-width: 70ch;
  color: var(--text);
  font-size: 16px;
  line-height: 1.8;
  text-align: justify;
  text-align-last: left;
  text-justify: inter-word;
}

.framework-signature {
  display: flex;
  flex-direction: column;
  gap: 3px;
  margin-top: 22px;
  padding: 13px 16px;
  border-left: 3px solid var(--purple);
  background: var(--bg-alt);
}

.framework-signature-label {
  color: var(--text-muted);
  font-size: 11px;
  font-weight: 800;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.framework-signature strong {
  color: var(--accent);
  font-size: 14px;
  line-height: 1.55;
}

.pdec-panel {
  padding: 22px;
  border: 1px solid #dce3ee;
  border-radius: 14px;
  background: #f8fbff;
  box-shadow: 0 12px 32px rgba(0, 48, 135, 0.07);
}

.pdec-panel-label {
  margin-bottom: 14px;
  color: var(--text-muted);
  font-size: 11px;
  font-weight: 800;
  letter-spacing: 0.07em;
  text-transform: uppercase;
}

.pdec-flow {
  display: grid;
  gap: 10px;
  list-style: none;
}

.pdec-step {
  --step-color: var(--accent);
  position: relative;
  display: grid;
  grid-template-columns: 42px minmax(0, 1fr);
  align-items: center;
  gap: 12px;
  min-height: 64px;
  padding: 10px 12px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: #fff;
}

.pdec-step[data-stage="D"] {
  --step-color: var(--teal);
}

.pdec-step[data-stage="E"] {
  --step-color: var(--amber);
}

.pdec-step[data-stage="C"] {
  --step-color: var(--purple);
}

.pdec-step:not(:last-child)::after {
  position: absolute;
  bottom: -11px;
  left: 32px;
  z-index: 1;
  width: 2px;
  height: 12px;
  background: #cbd6e5;
  content: "";
}

.pdec-letter {
  display: inline-flex;
  width: 38px;
  height: 38px;
  align-items: center;
  justify-content: center;
  border-radius: 9px;
  background: color-mix(in srgb, var(--step-color) 10%, white);
  color: var(--step-color);
  font-size: 16px;
  font-weight: 900;
}

.pdec-copy {
  display: flex;
  min-width: 0;
  flex-direction: column;
  gap: 2px;
}

.pdec-copy strong {
  color: var(--accent);
  font-size: 13px;
}

.pdec-copy span {
  color: var(--text-muted);
  font-size: 12px;
  line-height: 1.45;
}

/* Shared section structure */
.pi-section {
  padding: 48px 0;
}

.pi-section + .pi-section {
  border-top: 1px solid var(--border);
}

.pi-section--intro {
  padding-top: 38px;
  padding-bottom: 38px;
}

.pi-section--framework,
.pi-section--routing {
  background: #fbfcfe;
}

.section-heading-row {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: 32px;
  margin-bottom: 24px;
}

.section-heading-row--compact {
  margin-bottom: 20px;
}

.section-title {
  max-width: 780px;
  color: var(--accent);
  font-size: clamp(23px, 3vw, 31px);
  font-weight: 800;
  letter-spacing: -0.02em;
  line-height: 1.25;
  text-wrap: balance;
}

.section-summary {
  max-width: 430px;
  color: var(--text-muted);
  font-size: 13px;
  line-height: 1.7;
  text-align: right;
}

.research-thesis {
  display: grid;
  grid-template-columns: 76px minmax(0, 1fr);
  align-items: stretch;
  overflow: hidden;
  border: 1px solid var(--border);
  border-radius: 12px;
  background: #fff;
  box-shadow: 0 8px 24px rgba(0, 48, 135, 0.05);
}

.research-thesis-mark {
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--accent-light);
  color: var(--accent);
  font-size: 18px;
  font-weight: 900;
  letter-spacing: 0.05em;
}

.research-thesis p {
  padding: 22px 24px;
  font-size: 15px;
  line-height: 1.8;
  text-align: justify;
  text-align-last: left;
}

/* PDEC stage cards */
.framework-stages {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 18px;
}

.framework-stage {
  --stage-color: var(--accent);
  display: flex;
  min-width: 0;
  flex-direction: column;
  overflow: hidden;
  padding: 23px 23px 20px;
  border: 1px solid var(--border);
  border-top: 4px solid var(--stage-color);
  border-radius: 12px;
  background: #fff;
  box-shadow: 0 7px 22px rgba(0, 48, 135, 0.05);
}

.framework-stage.stage-d {
  --stage-color: var(--teal);
}

.framework-stage.stage-e {
  --stage-color: var(--amber);
}

.framework-stage.stage-c {
  --stage-color: var(--purple);
}

.stage-topline {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 15px;
}

.stage-index {
  color: var(--stage-color);
  font-size: 12px;
  font-weight: 900;
  letter-spacing: 0.1em;
}

.stage-name {
  color: var(--stage-color);
  font-size: 11px;
  font-weight: 800;
  letter-spacing: 0.06em;
  text-align: right;
  text-transform: uppercase;
}

.framework-stage h3 {
  min-height: 55px;
  margin-bottom: 10px;
  color: var(--accent);
  font-size: 20px;
  line-height: 1.35;
}

.framework-stage > p {
  min-height: 76px;
  margin-bottom: 15px;
  color: var(--text);
  font-size: 14px;
  line-height: 1.75;
  text-align: justify;
  text-align-last: left;
}

.stage-signals {
  display: grid;
  gap: 8px;
  margin: 0 0 20px;
  list-style: none;
}

.stage-signals li {
  position: relative;
  padding-left: 16px;
  color: var(--text-muted);
  font-size: 13px;
  line-height: 1.55;
}

.stage-signals li::before {
  position: absolute;
  top: 0.7em;
  left: 2px;
  width: 5px;
  height: 5px;
  border-radius: 50%;
  background: var(--stage-color);
  content: "";
  transform: translateY(-50%);
}

.stage-output {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 14px;
  margin-top: auto;
  padding-top: 14px;
  border-top: 1px solid var(--border);
}

.stage-output span {
  color: var(--text-muted);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.stage-output strong {
  color: var(--stage-color);
  font-size: 13px;
  text-align: right;
}

/* Failure taxonomy */
.weakness-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 14px;
}

.weakness-card {
  min-width: 0;
  padding: 19px 18px 20px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: #fff;
}

.weakness-code {
  display: inline-flex;
  width: 32px;
  height: 32px;
  align-items: center;
  justify-content: center;
  margin-bottom: 14px;
  border-radius: 8px;
  background: var(--accent-light);
  color: var(--accent);
  font-size: 13px;
  font-weight: 900;
}

.weakness-card h3 {
  min-height: 43px;
  margin-bottom: 8px;
  color: var(--accent);
  font-size: 15px;
  line-height: 1.4;
}

.weakness-card p {
  color: var(--text-muted);
  font-size: 13px;
  line-height: 1.65;
}

/* Risk routing */
.risk-axis {
  position: relative;
  display: flex;
  justify-content: space-between;
  margin-bottom: 16px;
  color: var(--text-muted);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.risk-axis::after {
  position: absolute;
  right: 0;
  bottom: -8px;
  left: 0;
  height: 2px;
  background: #dbe2ec;
  content: "";
}

.route-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 14px;
}

.route-card {
  --route-color: var(--green);
  min-width: 0;
  padding: 20px 18px;
  border: 1px solid var(--border);
  border-top: 3px solid var(--route-color);
  border-radius: 10px;
  background: #fff;
}

.route-card.route-tool {
  --route-color: var(--teal);
}

.route-card.route-llm {
  --route-color: var(--amber);
}

.route-card.route-human {
  --route-color: var(--purple);
}

.route-index {
  display: block;
  margin-bottom: 15px;
  color: var(--route-color);
  font-size: 11px;
  font-weight: 900;
  letter-spacing: 0.1em;
}

.route-card h3 {
  min-height: 45px;
  margin-bottom: 8px;
  color: var(--accent);
  font-size: 15px;
  line-height: 1.45;
}

.route-card p {
  color: var(--text-muted);
  font-size: 13px;
  line-height: 1.65;
}

.route-gate {
  margin-top: 18px;
  padding: 13px 16px;
  border-left: 3px solid var(--purple);
  background: #f3f0ff;
  color: #403a5e;
  font-size: 13px;
  font-weight: 650;
}

/* Outcome */
.pi-outcome {
  padding: 18px 0 54px;
  background: #fbfcfe;
}

.outcome-panel {
  display: grid;
  grid-template-columns: 110px minmax(0, 1fr);
  align-items: center;
  gap: 26px;
  padding: 28px 30px;
  border-radius: 14px;
  background: var(--accent);
  color: #fff;
}

.outcome-marker {
  display: flex;
  width: 92px;
  height: 92px;
  align-items: center;
  justify-content: center;
  border: 1px solid rgba(255, 255, 255, 0.35);
  border-radius: 50%;
  font-size: 16px;
  font-weight: 900;
  letter-spacing: 0.08em;
}

.outcome-panel .section-kicker {
  color: #9fddd8;
}

.outcome-panel h2 {
  margin-bottom: 8px;
  font-size: clamp(22px, 3vw, 30px);
  line-height: 1.3;
}

.outcome-panel p {
  max-width: 780px;
  color: rgba(255, 255, 255, 0.84);
  font-size: 14px;
  line-height: 1.75;
}

/* Back to top and footer */
#back-to-top {
  position: fixed;
  right: 28px;
  bottom: 32px;
  z-index: 999;
  display: flex;
  width: 44px;
  height: 44px;
  align-items: center;
  justify-content: center;
  border: 0;
  border-radius: 50%;
  background: var(--accent);
  color: #fff;
  cursor: pointer;
  font: 700 20px/1 var(--font);
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.3s ease, background-color 0.2s ease;
}

#back-to-top.visible {
  opacity: 1;
  pointer-events: auto;
}

#back-to-top:hover {
  background: var(--accent-dark);
}

.site-footer {
  padding: 18px 0 36px;
  border-top: 1px solid var(--border);
  background: #f8fbff;
}

.footer-shell {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 0 28px;
}

.footer-links {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 10px;
  padding-top: 14px;
}

.footer-link {
  display: inline-flex;
  align-items: center;
  padding: 7px 14px;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: #fff;
  color: var(--accent);
  font-size: 13px;
  font-weight: 600;
  text-decoration: none;
  transition: border-color 0.2s ease, background-color 0.2s ease;
}

.footer-link:hover {
  border-color: var(--accent);
  background: var(--accent-light);
}

.footer-bottom {
  margin-top: 10px;
  padding-top: 8px;
  color: var(--text-muted);
  font-size: 12px;
  text-align: center;
}

@media (max-width: 900px) {
  .pi-hero-grid {
    grid-template-columns: minmax(0, 1fr);
    gap: 28px;
  }

  .pdec-panel {
    padding: 18px;
  }

  .framework-stages {
    gap: 14px;
  }

  .weakness-grid,
  .route-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 760px) {
  .container {
    padding-right: 20px;
    padding-left: 20px;
  }

  .nav-inner {
    flex-wrap: wrap;
    gap: 10px;
  }

  .language-toggle {
    order: 2;
    margin-left: auto;
  }

  .nav-toggle {
    display: inline-flex;
    order: 3;
  }

  .nav-links {
    order: 4;
    flex-basis: 100%;
    flex-wrap: wrap;
    gap: 10px 16px;
  }

  .site-header.js-mobile-nav .nav-links {
    display: none;
    flex-direction: column;
    gap: 0;
    padding-top: 6px;
  }

  .site-header.nav-open .nav-links {
    display: flex;
  }

  .site-header.js-mobile-nav .nav-links a {
    padding: 8px 0;
    border-top: 1px solid var(--border);
  }

  .pi-hero {
    padding: 34px 0 32px;
  }

  .pi-hero-title {
    font-size: 34px;
  }

  .pi-hero-lead,
  .research-thesis p,
  .framework-stage > p {
    text-align: left;
    text-align-last: left;
  }

  .section-heading-row {
    align-items: flex-start;
    flex-direction: column;
    gap: 10px;
  }

  .section-summary {
    max-width: none;
    text-align: left;
  }

  .research-thesis {
    grid-template-columns: minmax(0, 1fr);
  }

  .research-thesis-mark {
    min-height: 50px;
  }

  .framework-stages {
    grid-template-columns: minmax(0, 1fr);
  }

  .framework-stage h3,
  .framework-stage > p {
    min-height: 0;
  }

  .outcome-panel {
    grid-template-columns: minmax(0, 1fr);
  }

  .outcome-marker {
    width: 72px;
    height: 72px;
  }

  .footer-shell {
    padding-right: 20px;
    padding-left: 20px;
  }
}

@media (max-width: 560px) {
  .weakness-grid,
  .route-grid {
    grid-template-columns: minmax(0, 1fr);
  }

  .pdec-panel {
    padding: 14px;
  }

  .pdec-step {
    grid-template-columns: 38px minmax(0, 1fr);
    padding-right: 10px;
    padding-left: 10px;
  }

  .pdec-letter {
    width: 34px;
    height: 34px;
  }

  .pdec-step:not(:last-child)::after {
    left: 28px;
  }

  .stage-output {
    align-items: flex-start;
    flex-direction: column;
    gap: 4px;
  }

  .stage-output strong {
    text-align: left;
  }

  .risk-axis {
    gap: 20px;
  }

  .risk-axis span:last-child {
    text-align: right;
  }

  #back-to-top {
    right: 18px;
    bottom: 22px;
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    transition-duration: 0.01ms !important;
  }
}