:root {
  --ink: #17242b;
  --muted: #52646d;
  --paper: #fbfcfa;
  --soft: #edf4f3;
  --line: #cbd9d7;
  --teal: #006b7e;
  --teal-dark: #004d5c;
  --coral: #c9583c;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: Georgia, "Times New Roman", serif;
  font-size: 1.08rem;
  line-height: 1.72;
}

.container {
  width: min(1100px, calc(100% - 2.5rem));
  margin-inline: auto;
}

h1, h2, h3, h4, h5, h6,
.eyebrow, .lesson-number, .lesson-nav, .site-footer, small {
  font-family: "Avenir Next", Avenir, "Century Gothic", sans-serif;
}

h1, h2, h3, h4, h5, h6 {
  line-height: 1.18;
  letter-spacing: 0;
}

h1 { margin: 0; font-size: clamp(2.6rem, 8vw, 5.5rem); }
h2 { font-size: clamp(1.7rem, 4vw, 2.5rem); }
h3 { margin-top: 2.5rem; font-size: 1.55rem; }
h4 { margin-top: 2rem; font-size: 1.25rem; }

a {
  color: var(--teal-dark);
  text-underline-offset: 0.15em;
}

a:hover { color: var(--coral); }

.site-header {
  border-bottom: 1px solid var(--line);
  background: var(--soft);
}

.masthead {
  display: grid;
  grid-template-columns: minmax(120px, 240px) 1fr;
  gap: clamp(1.5rem, 5vw, 4rem);
  align-items: center;
  min-height: min(62vh, 620px);
  padding-block: 4rem;
}

.brand-mark { width: 100%; height: auto; }

.lead {
  max-width: 700px;
  margin: 0.75rem 0 0;
  color: var(--muted);
  font-size: clamp(1.15rem, 2.5vw, 1.45rem);
}

.eyebrow {
  margin: 0 0 0.6rem;
  color: var(--teal);
  font-size: 0.76rem;
  font-weight: 700;
  text-transform: uppercase;
}

.intro-band {
  border-bottom: 1px solid var(--line);
  background: var(--ink);
  color: #f7faf8;
}

.intro-grid {
  display: grid;
  grid-template-columns: 2fr 1fr;
  gap: 4rem;
  padding-block: 3rem;
}

.intro-grid h2, .intro-grid p { margin-block: 0 0.75rem; }

.intro-grid aside {
  display: grid;
  align-content: center;
  border-left: 3px solid var(--coral);
  padding-left: 1.5rem;
}

.intro-grid aside strong { font-size: 1.35rem; }
.course-section { padding-block: 4rem 5rem; }
.section-heading { max-width: 720px; margin-bottom: 2rem; }
.section-heading h2 { margin: 0; }

.lesson-list {
  margin: 0;
  padding: 0;
  border-top: 1px solid var(--line);
  list-style: none;
}

.lesson-list li { border-bottom: 1px solid var(--line); }

.lesson-list a {
  display: grid;
  grid-template-columns: 4rem 1fr;
  gap: 1rem;
  align-items: start;
  padding: 1.5rem 0.75rem;
  color: inherit;
  text-decoration: none;
  transition: background-color 160ms ease, padding-left 160ms ease;
}

.lesson-list a:hover { padding-left: 1.15rem; background: var(--soft); }
.lesson-number { color: var(--coral); font-size: 0.85rem; font-weight: 700; }
.lesson-list strong, .lesson-list small { display: block; }
.lesson-list strong { font-size: 1.2rem; line-height: 1.3; }
.lesson-list small { margin-top: 0.35rem; color: var(--muted); font-size: 0.9rem; line-height: 1.5; }

.ecosystem-band {
  padding-block: 4rem;
  border-top: 1px solid var(--line);
  background: var(--soft);
}

.ecosystem-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  border-top: 1px solid var(--line);
  border-left: 1px solid var(--line);
}

.ecosystem-grid article {
  padding: 1.5rem;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
}

.ecosystem-grid h3 {
  margin: 0.35rem 0 0.6rem;
  font-size: 1.3rem;
}

.ecosystem-grid p { margin: 0; }

.ecosystem-label {
  color: var(--coral);
  font-family: "Avenir Next", Avenir, sans-serif;
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
}

.ecosystem-flow {
  margin: 1.5rem 0 0;
  color: var(--teal-dark);
  font-family: "Avenir Next", Avenir, sans-serif;
  font-size: 0.92rem;
  font-weight: 600;
  text-align: center;
}

.author-section {
  padding-block: 4rem;
  border-top: 1px solid var(--line);
}

.author-grid {
  display: grid;
  grid-template-columns: minmax(250px, 0.8fr) minmax(0, 1.2fr);
  gap: clamp(2rem, 7vw, 6rem);
  align-items: start;
}

.author-grid h2 { margin: 0; }

.author-role {
  max-width: 480px;
  color: var(--muted);
  font-family: "Avenir Next", Avenir, sans-serif;
  line-height: 1.55;
}

.author-copy > p { margin-top: 0; }

.author-links {
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem 1.25rem;
  font-family: "Avenir Next", Avenir, sans-serif;
  font-size: 0.88rem;
  font-weight: 600;
}

.site-footer {
  padding-block: 2rem;
  background: var(--ink);
  border-top: 1px solid var(--line);
  color: #dbe5e2;
  font-size: 0.85rem;
}

.footer-inner {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  align-items: center;
}

.footer-inner nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem 1rem;
}

.site-footer a { color: #f7faf8; }

.lesson-header {
  max-width: 820px;
  padding-block: 2.5rem 2rem;
  border-bottom: 1px solid var(--line);
}

.lesson-header h1 { font-size: clamp(2.2rem, 6vw, 4rem); }

.back-link {
  display: inline-block;
  margin-bottom: 3rem;
  font-family: "Avenir Next", Avenir, sans-serif;
  font-size: 0.88rem;
  font-weight: 600;
  text-decoration: none;
}

.lesson-layout { max-width: 820px; padding-block: 2rem 5rem; }
.lesson-content > :first-child { margin-top: 0; }
.lesson-content img, .lesson-content figure, .lesson-content video, .lesson-content iframe { max-width: 100%; }
.lesson-content img { height: auto; }
.lesson-content figure { margin: 2rem 0; }

.lesson-content figcaption, .lesson-content .image-caption {
  color: var(--muted);
  font-family: "Avenir Next", Avenir, sans-serif;
  font-size: 0.82rem;
  line-height: 1.45;
}

.lesson-content blockquote {
  margin: 2rem 0;
  border-left: 3px solid var(--coral);
  padding: 0.25rem 0 0.25rem 1.5rem;
  color: #34474f;
  font-size: 1.15rem;
}

.lesson-content pre, .lesson-content code { font-family: "SFMono-Regular", Consolas, monospace; }

.lesson-content pre {
  overflow-x: auto;
  padding: 1rem;
  background: #e7eeed;
  font-size: 0.88rem;
  line-height: 1.5;
}

.lesson-content table { display: block; max-width: 100%; overflow-x: auto; border-collapse: collapse; }
.lesson-content th, .lesson-content td { padding: 0.6rem; border: 1px solid var(--line); }
.lesson-content .button-wrapper, .lesson-content .subscription-widget-wrap-editor,
.lesson-content .subscribe-widget, .lesson-content .paywall { display: none; }

.lesson-nav {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 4rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--line);
  font-size: 0.9rem;
  font-weight: 600;
}

@media (max-width: 650px) {
  .container { width: min(100% - 1.5rem, 1100px); }
  .masthead { grid-template-columns: 72px 1fr; gap: 1.25rem; min-height: auto; padding-block: 3rem; }
  .intro-grid { grid-template-columns: 1fr; gap: 1.25rem; }
  .lesson-list a { grid-template-columns: 2.5rem 1fr; padding-inline: 0; }
  .ecosystem-grid { grid-template-columns: 1fr; }
  .author-grid { grid-template-columns: 1fr; gap: 1.5rem; }
  .footer-inner { align-items: flex-start; flex-direction: column; }
  .lesson-nav { align-items: flex-start; }
}