:root {
  --paper: #f4efe4;
  --paper-deep: #e7dfd1;
  --plate: #fbf7f0;
  --ink: #1c1916;
  --muted: #5a5148;
  --line: #d2c8b8;
  --accent: #1b4332;
  --signal: #8f3419;
  --serif: "Fraunces", "Iowan Old Style", "Palatino Linotype", Palatino, Georgia, serif;
  --sans: "Source Sans 3", "Segoe UI", sans-serif;
  --measure: 40rem;
}

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

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 1.125rem;
  line-height: 1.6;
  text-rendering: optimizeLegibility;
}

main {
  flex: 1 0 auto;
}

p {
  margin: 0 0 0.9rem;
}

p:last-child {
  margin-bottom: 0;
}

h1,
h2,
h3 {
  font-family: var(--serif);
  font-weight: 560;
  letter-spacing: -0.03em;
  line-height: 1.05;
}

h1 {
  margin: 0 0 1rem;
  font-size: clamp(2.5rem, 5vw, 4.25rem);
}

h2 {
  margin: 0 0 0.75rem;
  font-size: clamp(1.7rem, 2.4vw, 2.15rem);
  line-height: 1.15;
}

h3 {
  margin: 0 0 0.35rem;
  font-size: 1.45rem;
  line-height: 1.2;
}

a {
  color: var(--accent);
  text-underline-offset: 0.18em;
}

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

:focus-visible {
  outline: 2px solid var(--signal);
  outline-offset: 3px;
}

::selection {
  background: #e7c3b4;
  color: var(--ink);
}

.skip {
  position: absolute;
  left: 1rem;
  top: -4rem;
  z-index: 5;
  background: var(--ink);
  color: var(--paper);
  padding: 0.5rem 0.75rem;
  text-decoration: none;
}

.skip:focus {
  top: 0.75rem;
}

.wrap {
  width: min(72rem, calc(100% - 2rem));
  margin-inline: auto;
}

.math {
  font-family: var(--serif);
  font-style: italic;
  font-weight: 500;
  white-space: nowrap;
}

.kicker,
.num,
.status {
  margin: 0;
}

.kicker {
  margin-bottom: 0.9rem;
  color: var(--accent);
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.16em;
  text-transform: uppercase;
}

.section-label {
  margin-bottom: 0;
  padding-top: 1.35rem;
}

.num {
  color: var(--signal);
  font-family: var(--serif);
  font-size: 1.35rem;
  line-height: 1;
}

.masthead {
  position: relative;
  border-top: 3px solid var(--ink);
  border-bottom: 1px solid var(--ink);
  padding-top: 8px;
  background: var(--paper);
}

.masthead::before {
  content: "";
  position: absolute;
  top: 2px;
  left: 0;
  right: 0;
  border-top: 1px solid var(--ink);
}

.masthead-inner {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  min-height: 4.25rem;
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.7rem;
  min-width: 0;
  color: inherit;
  font-family: var(--serif);
  font-size: 1.12rem;
  font-weight: 560;
  letter-spacing: -0.02em;
  line-height: 1.1;
  text-decoration: none;
}

a.brand:hover {
  color: inherit;
}

.mark {
  width: 1.7rem;
  height: 1.7rem;
  flex: none;
}

.nav {
  display: flex;
  align-items: center;
  gap: 1.6rem;
}

.nav a {
  color: var(--ink);
  font-size: 0.92rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-decoration: none;
  text-transform: uppercase;
}

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

.nav a[aria-current="page"] {
  box-shadow: inset 0 -2px 0 var(--signal);
}

.nav-toggle {
  display: none;
  min-height: 2.75rem;
  padding: 0.35rem 0.8rem;
  border: 1px solid var(--ink);
  background: transparent;
  color: var(--ink);
  font: 600 0.85rem/1 var(--sans);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  cursor: pointer;
}

.hero {
  display: grid;
  grid-template-columns: minmax(0, 1.15fr) minmax(16rem, 0.85fr);
  gap: 3rem;
  align-items: center;
  padding: 4.25rem 0 3.5rem;
}

.hero h1 {
  max-width: 11ch;
  font-size: clamp(3rem, 6.2vw, 5.35rem);
  line-height: 0.94;
}

.lede {
  max-width: 38rem;
  color: var(--muted);
  font-size: 1.28rem;
  line-height: 1.5;
}

.btn {
  display: inline-block;
  margin-top: 0.4rem;
  padding: 0.75rem 1.05rem;
  background: var(--ink);
  color: var(--paper);
  font-weight: 600;
  text-decoration: none;
  transition: background-color 0.15s linear;
}

.btn:hover {
  background: var(--accent);
  color: var(--paper);
}

.diagram {
  margin: 0;
  padding: 0.85rem 0.85rem 0.8rem;
  border: 1px solid var(--ink);
  background: var(--plate);
}

.diagram svg {
  display: block;
  width: 100%;
  height: auto;
}

.diagram figcaption {
  margin: 0.7rem 0.15rem 0.15rem;
  color: var(--muted);
  font-family: var(--serif);
  font-style: italic;
  font-size: 1.02rem;
  line-height: 1.4;
}

.rule-block {
  border-top: 1px solid var(--ink);
  border-bottom: 1px solid var(--ink);
}

.principles {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
}

.principles article {
  padding: 1.6rem 1.5rem 1.8rem 0;
}

.principles article + article {
  padding-left: 1.5rem;
  border-left: 1px solid var(--line);
}

.principles .num {
  display: block;
  margin-bottom: 0.85rem;
}

.principles h2 {
  font-size: 1.55rem;
}

.band {
  margin-top: 3rem;
  background: var(--paper-deep);
  border-top: 1px solid var(--ink);
  border-bottom: 1px solid var(--ink);
}

.course-feature {
  display: grid;
  grid-template-columns: 4.5rem minmax(0, 1fr) auto;
  gap: 1rem 1.5rem;
  align-items: center;
  padding: 2.1rem 0;
}

.course-feature h2 {
  margin-bottom: 0.4rem;
}

.course-feature p {
  max-width: var(--measure);
  color: var(--muted);
}

.page-head {
  padding: 3.25rem 0 0.5rem;
}

.page-head h1 {
  max-width: 16ch;
}

.crumbs {
  margin: 0 0 1.15rem;
  color: var(--muted);
  font-size: 0.98rem;
}

.crumbs a {
  color: var(--muted);
}

.facts {
  display: flex;
  flex-wrap: wrap;
  gap: 1.25rem 2.5rem;
  margin: 2rem 0 0;
  padding: 1rem 0;
  border-top: 1px solid var(--ink);
  border-bottom: 1px solid var(--ink);
}

.facts dt {
  color: var(--muted);
  font-size: 0.75rem;
  font-weight: 600;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.facts dd {
  margin: 0.25rem 0 0;
  font-family: var(--serif);
  font-size: 1.3rem;
  letter-spacing: -0.02em;
}

.split {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 3rem;
  padding: 2.25rem 0 0.5rem;
}

.split p,
.ticks {
  color: var(--ink);
}

.ticks {
  margin: 0;
  padding-left: 1.15rem;
}

.ticks li {
  margin: 0.45rem 0;
  padding-left: 0.2rem;
}

.ticks li::marker {
  color: var(--accent);
}

.syllabus-block {
  padding-top: 2.5rem;
}

.syllabus-block .lede {
  margin-bottom: 0.25rem;
  font-size: 1.15rem;
}

.lessons {
  list-style: none;
  margin: 1.25rem 0 0;
  padding: 0;
  counter-reset: lesson;
}

.lessons li {
  display: grid;
  grid-template-columns: 4rem minmax(0, 1fr);
  gap: 0.5rem 1rem;
  padding: 1.2rem 0;
  border-top: 1px solid var(--line);
  counter-increment: lesson;
}

.lessons li:last-child {
  border-bottom: 1px solid var(--line);
}

.lessons li::before {
  content: counter(lesson, decimal-leading-zero);
  color: var(--signal);
  font-family: var(--serif);
  font-size: 1.35rem;
  line-height: 1.15;
}

.lessons p {
  max-width: 42rem;
  color: var(--muted);
}

.study {
  max-width: var(--measure);
  margin-top: 2.5rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--ink);
}

.catalog {
  padding-bottom: 3rem;
}

.catalog-item {
  display: grid;
  grid-template-columns: 4.5rem minmax(0, 1fr);
  gap: 0.4rem 1.5rem;
  margin-top: 2rem;
  padding: 1.8rem 0 2rem;
  border-top: 1px solid var(--ink);
  border-bottom: 1px solid var(--ink);
}

.catalog-item .num {
  font-size: 2rem;
}

.catalog-item h2 {
  margin-top: 0.35rem;
}

.status {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  color: var(--accent);
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.status::before {
  content: "";
  width: 0.55rem;
  height: 0.55rem;
  background: var(--accent);
}

.catalog-item .summary {
  max-width: 40rem;
  margin-top: 0.7rem;
  color: var(--muted);
}

.site-footer {
  border-top: 1px solid var(--ink);
  padding: 1.2rem 0 1.8rem;
}

.footer-inner {
  display: flex;
  justify-content: space-between;
  gap: 0.5rem 1.5rem;
  flex-wrap: wrap;
  color: var(--muted);
  font-size: 0.98rem;
}

.section-pad {
  padding-bottom: 4rem;
}

@media (max-width: 800px) {
  .hero,
  .principles,
  .split,
  .course-feature {
    grid-template-columns: 1fr;
  }

  .hero {
    gap: 2rem;
    padding-top: 2.5rem;
  }

  .hero h1 {
    max-width: none;
  }

  .principles article {
    padding-right: 0;
  }

  .principles article + article {
    margin-top: 0.25rem;
    padding-top: 1.35rem;
    padding-left: 0;
    border-left: 0;
    border-top: 1px solid var(--line);
  }

  .course-feature {
    padding: 1.6rem 0;
  }

  .facts {
    flex-direction: column;
    gap: 1rem;
  }
}

@media (max-width: 720px) {
  .js .nav-toggle {
    display: inline-flex;
    align-items: center;
    justify-content: center;
  }

  .js .nav {
    display: none;
    position: absolute;
    z-index: 3;
    top: calc(100% + 1px);
    left: 50%;
    width: 100vw;
    margin-left: -50vw;
    flex-direction: column;
    align-items: flex-start;
    gap: 0;
    padding: 0.35rem 1rem 0.85rem;
    border-bottom: 1px solid var(--ink);
    background: var(--paper);
  }

  .js .nav.is-open {
    display: flex;
  }

  .js .nav a {
    padding: 0.7rem 0;
    font-size: 1rem;
  }
}

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

  .btn {
    transition: none;
  }
}

@media print {
  .nav-toggle {
    display: none !important;
  }

  .nav {
    display: flex !important;
    position: static !important;
    width: auto !important;
    margin-left: 0 !important;
    border: 0 !important;
    padding: 0 !important;
  }

  body {
    background: #fff;
  }

  .btn {
    background: transparent;
    color: var(--ink);
    padding-left: 0;
  }
}