:root {
  --ink: #121212;
  --muted: #5f6470;
  --paper: #ffffff;
  --line: #d8dde5;
  --blue: #1768c2;
  --blue-soft: #edf5ff;
  --yellow: #e6ae18;
  --yellow-soft: #fff9dc;
  --green: #208348;
  --green-soft: #edf9f1;
  --shadow: 0 20px 50px rgba(20, 28, 38, 0.1);
  color-scheme: light;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: Georgia, "Times New Roman", serif;
  line-height: 1.55;
}

a {
  color: inherit;
  text-decoration: none;
}

.site-header,
.site-footer,
main > section {
  width: min(1160px, calc(100% - 40px));
  margin: 0 auto;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  padding: 18px 0 16px;
  background: rgba(255, 255, 255, 0.92);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(12px);
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 14px;
  min-width: 230px;
}

.brand-mark {
  display: grid;
  width: 48px;
  height: 48px;
  place-items: center;
  border: 2px solid var(--ink);
  font-family: Arial, sans-serif;
  font-size: 16px;
  font-weight: 700;
  letter-spacing: 0;
}

.brand strong,
.brand small {
  display: block;
}

.brand strong {
  font-size: 16px;
  line-height: 1.2;
}

.brand small {
  color: var(--muted);
  font-size: 13px;
}

nav {
  display: flex;
  flex-wrap: wrap;
  justify-content: flex-end;
  gap: 6px 22px;
  font-family: Arial, sans-serif;
  font-size: 14px;
}

nav a {
  border-bottom: 2px solid transparent;
  padding: 8px 0;
}

nav a:hover,
nav a:focus-visible {
  border-color: var(--blue);
  outline: none;
}

main > section {
  border-bottom: 1px solid var(--line);
  padding: 58px 0;
}

.section-grid {
  display: grid;
  grid-template-columns: minmax(0, 0.92fr) minmax(320px, 1.08fr);
  gap: 54px;
  align-items: center;
}

.hero {
  min-height: 720px;
  padding-top: 72px;
  padding-bottom: 72px;
}

h1,
h2,
h3,
p {
  margin-top: 0;
}

h1 {
  margin-bottom: 14px;
  font-size: clamp(76px, 12vw, 156px);
  font-weight: 700;
  line-height: 0.88;
}

h2 {
  margin-bottom: 16px;
  font-size: clamp(34px, 5vw, 54px);
  font-weight: 500;
  line-height: 1.06;
}

h3 {
  margin-bottom: 8px;
  font-size: 22px;
  line-height: 1.2;
}

p {
  color: var(--muted);
  font-size: 18px;
}

.lede {
  color: var(--ink);
  font-size: clamp(22px, 3vw, 32px);
  line-height: 1.22;
}

.hero-copy::after {
  content: "";
  display: block;
  width: min(360px, 100%);
  height: 4px;
  margin: 28px 0;
  background: linear-gradient(
    90deg,
    var(--blue) 0 34%,
    var(--yellow) 34% 66%,
    var(--green) 66% 100%
  );
}

.actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 28px;
  font-family: Arial, sans-serif;
}

.actions a,
.site-footer > a {
  display: inline-flex;
  align-items: center;
  min-height: 44px;
  border: 1px solid var(--ink);
  padding: 10px 16px;
  font-size: 14px;
  font-weight: 700;
}

.actions a:first-child {
  background: var(--ink);
  color: #fff;
}

.actions a:hover,
.actions a:focus-visible,
.site-footer > a:hover,
.site-footer > a:focus-visible {
  border-color: var(--blue);
  box-shadow: 0 0 0 3px rgba(23, 104, 194, 0.16);
  outline: none;
}

.atlas-frame {
  margin: 0;
  border: 1px solid var(--line);
  border-radius: 8px;
  background:
    linear-gradient(rgba(23, 104, 194, 0.06) 1px, transparent 1px),
    linear-gradient(90deg, rgba(23, 104, 194, 0.06) 1px, transparent 1px), #fff;
  background-size: 24px 24px;
  box-shadow: var(--shadow);
  overflow: hidden;
}

.atlas-frame img {
  display: block;
  width: 100%;
  aspect-ratio: 1.44;
  object-fit: cover;
  object-position: 54% 7%;
}

.atlas-frame figcaption {
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-family: Arial, sans-serif;
  font-size: 13px;
  padding: 12px 14px;
}

.start-here {
  padding-top: 46px;
}

.start-grid {
  display: grid;
  grid-template-columns: repeat(5, minmax(120px, 1fr));
  gap: 14px;
  margin-top: 28px;
  font-family: Arial, sans-serif;
}

.start-grid a {
  display: flex;
  align-items: center;
  min-height: 76px;
  border: 1px solid var(--line);
  border-left: 4px solid var(--blue);
  padding: 16px;
  background: #fff;
  font-weight: 700;
  box-shadow: 0 10px 24px rgba(20, 28, 38, 0.06);
}

.start-grid a:nth-child(2) {
  border-left-color: var(--yellow);
}

.start-grid a:nth-child(3),
.start-grid a:nth-child(4) {
  border-left-color: var(--green);
}

.start-grid a:hover,
.start-grid a:focus-visible {
  border-color: var(--blue);
  border-left-color: var(--blue);
  box-shadow: 0 0 0 3px rgba(23, 104, 194, 0.16);
  outline: none;
}

.model {
  align-items: stretch;
}

.loop-diagram {
  position: relative;
  min-height: 430px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background:
    radial-gradient(
      circle at center,
      rgba(23, 104, 194, 0.08) 0 2px,
      transparent 3px
    ),
    #fff;
  background-size: 28px 28px;
}

.loop-diagram::before {
  content: "";
  position: absolute;
  inset: 72px;
  border: 2px dashed #9aa6b2;
  border-radius: 50%;
}

.loop-center,
.loop-node {
  position: absolute;
  display: grid;
  place-items: center;
  border: 1px solid var(--line);
  background: #fff;
  text-align: center;
}

.loop-center {
  inset: 50%;
  width: 112px;
  height: 112px;
  margin: -56px 0 0 -56px;
  border-radius: 50%;
  color: var(--ink);
  font-size: 18px;
}

.loop-node {
  width: 138px;
  min-height: 54px;
  border-radius: 6px;
  font-family: Arial, sans-serif;
  font-size: 14px;
  font-weight: 700;
}

.node-blue {
  top: 54px;
  left: 50%;
  margin-left: -69px;
  border-color: var(--blue);
  color: var(--blue);
}

.node-yellow {
  right: 36px;
  top: 50%;
  margin-top: -27px;
  border-color: var(--yellow);
  color: #8a6200;
}

.node-green {
  bottom: 54px;
  left: 50%;
  margin-left: -69px;
  border-color: var(--green);
  color: var(--green);
}

.node-ink {
  left: 36px;
  top: 50%;
  margin-top: -27px;
  border-color: var(--ink);
}

.steps {
  padding-left: 20px;
  color: var(--muted);
  font-size: 17px;
}

.steps li + li {
  margin-top: 10px;
}

.section-heading {
  max-width: 760px;
  margin-bottom: 28px;
}

.book-spine,
.layer-grid,
.link-list {
  display: grid;
  gap: 18px;
}

.book-spine {
  grid-template-columns: repeat(4, minmax(0, 1fr));
  counter-reset: parts;
}

.book-spine article,
.layer,
.link-list a,
.concept {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
}

.book-spine article {
  min-height: 230px;
  padding: 22px;
}

.book-spine span {
  display: inline-grid;
  width: 42px;
  height: 42px;
  place-items: center;
  margin-bottom: 34px;
  border: 1px solid currentColor;
  border-radius: 50%;
  color: var(--blue);
  font-family: Arial, sans-serif;
  font-weight: 700;
}

.book-spine article:nth-child(2) span {
  color: var(--yellow);
}

.book-spine article:nth-child(3) span,
.book-spine article:nth-child(4) span {
  color: var(--green);
}

.book-spine p,
.layer p,
.link-list span,
.concept span {
  font-size: 15px;
}

.layer-grid {
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.layer {
  min-height: 190px;
  padding: 28px;
}

.layer-blue {
  border-color: var(--blue);
  background: var(--blue-soft);
}

.layer-yellow {
  border-color: var(--yellow);
  background: var(--yellow-soft);
}

.layer-green {
  border-color: var(--green);
  background: var(--green-soft);
}

.link-list {
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.link-list a {
  display: block;
  min-height: 150px;
  padding: 22px;
  transition:
    transform 160ms ease,
    border-color 160ms ease,
    box-shadow 160ms ease;
}

.link-list a:hover,
.link-list a:focus-visible,
.concept:hover,
.concept:focus-visible {
  border-color: var(--blue);
  box-shadow: 0 10px 28px rgba(23, 104, 194, 0.14);
  outline: none;
  transform: translateY(-2px);
}

.link-list strong,
.concept strong {
  display: block;
  margin-bottom: 10px;
  font-size: 20px;
  line-height: 1.2;
}

.link-list span,
.concept span {
  display: block;
  color: var(--muted);
}

.concept-map {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 16px;
}

.concept {
  min-height: 150px;
  padding: 20px;
  transition:
    transform 160ms ease,
    border-color 160ms ease,
    box-shadow 160ms ease;
}

.concept-blue {
  border-color: var(--blue);
}

.concept-yellow {
  border-color: var(--yellow);
}

.concept-green {
  border-color: var(--green);
}

.concept-ink {
  border-color: var(--ink);
}

.site-footer {
  display: grid;
  grid-template-columns: 1.2fr 1fr auto;
  gap: 28px;
  align-items: center;
  padding: 28px 0 40px;
}

.site-footer p {
  margin: 0;
  font-size: 15px;
}

@media (max-width: 900px) {
  .site-header {
    position: static;
    align-items: flex-start;
    flex-direction: column;
  }

  nav {
    justify-content: flex-start;
  }

  .section-grid,
  .start-grid,
  .book-spine,
  .layer-grid,
  .link-list,
  .site-footer {
    grid-template-columns: 1fr;
  }

  .hero {
    min-height: 0;
    padding-top: 42px;
    padding-bottom: 42px;
  }

  .atlas-frame img {
    aspect-ratio: 1.15;
  }
}

@media (max-width: 560px) {
  .site-header,
  .site-footer,
  main > section {
    width: min(100% - 24px, 1160px);
  }

  main > section {
    padding: 42px 0;
  }

  .brand {
    min-width: 0;
  }

  .brand-mark {
    width: 42px;
    height: 42px;
  }

  .actions {
    display: grid;
  }

  .loop-diagram {
    min-height: 360px;
  }

  .loop-diagram::before {
    inset: 60px;
  }

  .loop-node {
    width: 112px;
    font-size: 12px;
  }

  .node-blue,
  .node-green {
    margin-left: -56px;
  }

  .node-yellow {
    right: 12px;
  }

  .node-ink {
    left: 12px;
  }

  .start-grid,
  .concept-map {
    grid-template-columns: 1fr;
  }
}