:root {
  --paper: #f5f0e7;
  --paper-deep: #e9dfd0;
  --ink: #172c3b;
  --ink-soft: #53636a;
  --red: #c84c3d;
  --red-dark: #9f352d;
  --teal: #1f746b;
  --teal-dark: #145850;
  --teal-soft: #e4efeb;
  --card: #fffdf8;
  --line: #d7ccbc;
  --white: #fffefa;
  --shadow: 0 1rem 2.5rem rgba(23, 44, 59, 0.08);
  --radius: 1.25rem;
}

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

html {
  background: var(--paper);
  color: var(--ink);
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background:
    linear-gradient(rgba(23, 44, 59, 0.03) 1px, transparent 1px),
    var(--paper);
  background-size: 100% 2.25rem;
  font-family: "Yu Gothic", "Hiragino Kaku Gothic ProN", "Noto Sans JP", sans-serif;
  font-size: 1rem;
  line-height: 1.8;
  overflow-x: hidden;
}

a {
  color: inherit;
}

a:focus-visible,
button:focus-visible {
  outline: 0.2rem solid var(--red);
  outline-offset: 0.25rem;
}

.skip-link {
  position: absolute;
  top: 0.75rem;
  left: 0.75rem;
  z-index: 5;
  padding: 0.5rem 0.8rem;
  border-radius: 0.4rem;
  background: var(--ink);
  color: var(--white);
  transform: translateY(-180%);
}

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

.site-shell {
  width: min(calc(100% - 2rem), 76rem);
  margin: 0 auto;
}

.site-header {
  padding: 1.5rem 0 4.5rem;
  border-top: 0.45rem solid var(--red);
}

.masthead {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding-bottom: 3rem;
  border-bottom: 1px solid var(--line);
}

.wordmark,
.edition {
  margin: 0;
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.12em;
}

.wordmark {
  display: inline-flex;
  align-items: center;
  gap: 0.65rem;
  text-transform: uppercase;
}

.wordmark::before {
  display: block;
  width: 0.75rem;
  height: 0.75rem;
  border-radius: 50%;
  background: var(--red);
  content: "";
}

.edition {
  color: var(--ink-soft);
}

.back-link,
.course-nav a {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  color: var(--teal-dark);
  font-size: 0.9rem;
  font-weight: 800;
  text-decoration: none;
}

.back-link {
  margin-top: 1.4rem;
  padding-bottom: 0.1rem;
  border-bottom: 2px solid var(--teal);
}

.back-link:hover,
.course-nav a:hover {
  color: var(--red-dark);
}

.hero {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(16rem, 20rem);
  align-items: end;
  gap: clamp(2rem, 7vw, 8rem);
  padding-top: 3.75rem;
}

.hero-kicker,
.section-kicker {
  margin: 0 0 1rem;
  color: var(--red-dark);
  font-size: 0.75rem;
  font-weight: 800;
  letter-spacing: 0.16em;
  text-transform: uppercase;
}

h1,
h2,
h3,
h4,
p {
  margin-top: 0;
}

h1 {
  max-width: 18ch;
  margin-bottom: 1.25rem;
  font-size: clamp(2.35rem, 6vw, 5rem);
  font-weight: 800;
  letter-spacing: -0.07em;
  line-height: 1.08;
  text-wrap: balance;
  overflow-wrap: anywhere;
}

.hero-lead {
  max-width: 48rem;
  margin-bottom: 1rem;
  color: var(--ink-soft);
  font-size: clamp(1.05rem, 1.8vw, 1.25rem);
  font-weight: 700;
  line-height: 1.85;
}

.hero-copy > p:last-of-type {
  max-width: 52rem;
  margin-bottom: 0;
  color: var(--ink-soft);
}

.notebook-link {
  max-width: 52rem;
  margin-top: 1.5rem;
  padding: 1rem 1.25rem;
  border-left: 0.35rem solid var(--teal);
  border-radius: 0 0.8rem 0.8rem 0;
  background: var(--teal-soft);
}

.notebook-link__label {
  margin-bottom: 0.35rem;
}

.notebook-link__anchor {
  color: var(--teal-dark);
  font-weight: 800;
  text-decoration: underline;
  text-decoration-thickness: 0.12rem;
  text-underline-offset: 0.18rem;
}

.notebook-link__anchor:hover {
  color: var(--red-dark);
}

.notebook-link p:last-child {
  margin-bottom: 0;
  color: var(--ink-soft);
  font-size: 0.9rem;
}

.hero-summary {
  position: relative;
  padding: 1.6rem;
  border-radius: var(--radius);
  background: var(--ink);
  box-shadow: var(--shadow);
  color: var(--white);
}

.hero-summary::after {
  position: absolute;
  right: 1.15rem;
  bottom: 1.15rem;
  width: 2.4rem;
  height: 2.4rem;
  border-right: 0.18rem solid var(--red);
  border-bottom: 0.18rem solid var(--red);
  content: "";
}

.summary-label {
  margin-bottom: 1.25rem;
  color: #b8d6cf;
  font-size: 0.75rem;
  font-weight: 800;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.summary-stats {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1rem;
  margin: 0;
}

.summary-stats div {
  display: flex;
  flex-direction: column;
  min-width: 0;
  padding-top: 0.75rem;
  border-top: 1px solid rgba(255, 254, 250, 0.35);
}

.summary-stats dt {
  order: 2;
  color: #d9e6e2;
  font-size: 0.78rem;
  line-height: 1.5;
}

.summary-stats dd {
  order: 1;
  margin: 0 0 0.15rem;
  color: #f6c5bc;
  font-family: Georgia, "Times New Roman", serif;
  font-size: clamp(2.8rem, 6vw, 4.6rem);
  font-weight: 700;
  line-height: 1;
}

main {
  display: grid;
  gap: 4.5rem;
  padding-bottom: 5rem;
}

.course-overview,
.lessons-section {
  min-width: 0;
}

.section-heading {
  display: grid;
  grid-template-columns: minmax(0, 0.8fr) minmax(0, 1.2fr);
  align-items: end;
  gap: 2rem;
  margin-bottom: 2rem;
  padding-bottom: 1.35rem;
  border-bottom: 2px solid var(--ink);
}

.section-kicker {
  margin-bottom: 0;
  color: var(--teal-dark);
}

h2 {
  margin-bottom: 0;
  font-size: clamp(1.8rem, 4vw, 3.2rem);
  letter-spacing: -0.06em;
  line-height: 1.15;
  overflow-wrap: anywhere;
}

h2 span {
  color: var(--red);
}

.section-heading p:last-child {
  max-width: 38rem;
  margin: 0;
  color: var(--ink-soft);
}

.course-purpose {
  max-width: 60rem;
  margin-bottom: 1.5rem;
  padding: clamp(1.25rem, 3vw, 2rem);
  border-left: 0.45rem solid var(--red);
  border-radius: 0 1rem 1rem 0;
  background: var(--card);
  box-shadow: 0 0.5rem 1.2rem rgba(23, 44, 59, 0.035);
}

.course-purpose-label {
  margin-bottom: 0.45rem;
  color: var(--red-dark);
  font-size: 0.8rem;
  font-weight: 800;
  letter-spacing: 0.08em;
}

.course-purpose-text {
  margin-bottom: 0;
  color: var(--ink);
  font-size: 1.1rem;
  font-weight: 700;
  line-height: 1.8;
}

.study-guidance {
  max-width: 60rem;
  margin-bottom: 1.5rem;
  padding: 1rem 1.25rem;
  border-left: 0.35rem solid var(--teal);
  border-radius: 0 0.8rem 0.8rem 0;
  background: var(--teal-soft);
}

.study-guidance h3 {
  margin-bottom: 0.35rem;
  color: var(--teal-dark);
  font-size: 1rem;
}

.study-guidance p {
  max-width: 56rem;
  margin-bottom: 0;
  color: var(--ink-soft);
}

.official-course-summary {
  max-width: 60rem;
  margin-bottom: 2rem;
  color: var(--ink-soft);
  font-size: 0.92rem;
}

.official-course-summary summary {
  color: var(--teal-dark);
  cursor: pointer;
  font-weight: 800;
}

.official-course-summary p {
  margin: 0.7rem 0 0;
}

.course-facts {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1rem;
  margin: 0;
}

.course-facts > div {
  min-width: 0;
  padding: 1.1rem 1.25rem;
  border: 1px solid var(--line);
  border-radius: 0.8rem;
  background: rgba(255, 253, 248, 0.7);
}

.course-facts dt {
  margin-bottom: 0.3rem;
  color: var(--ink-soft);
  font-size: 0.78rem;
  font-weight: 800;
  letter-spacing: 0.08em;
}

.course-facts dd {
  margin: 0;
  overflow-wrap: anywhere;
}

.translation-note {
  margin: 1.5rem 0 0;
  padding: 1rem 1.25rem;
  border-left: 0.35rem solid var(--teal);
  background: var(--teal-soft);
  color: var(--ink-soft);
}

.lesson-list {
  display: grid;
  gap: 1rem;
  margin: 0;
  padding: 0;
  list-style: none;
}

.lesson-card {
  display: grid;
  grid-template-columns: 5rem minmax(0, 1fr);
  min-width: 0;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--card);
  box-shadow: 0 0.5rem 1.2rem rgba(23, 44, 59, 0.035);
}

.lesson-number {
  display: flex;
  align-items: flex-start;
  justify-content: center;
  min-width: 0;
  padding: 1.5rem 0.5rem;
  background: var(--ink);
  color: var(--white);
  font-family: Georgia, "Times New Roman", serif;
  font-size: clamp(2rem, 5vw, 3.5rem);
  font-weight: 700;
  letter-spacing: -0.08em;
  line-height: 1;
}

.lesson-body {
  min-width: 0;
  padding: clamp(1.35rem, 3vw, 2rem) clamp(1.2rem, 4vw, 3rem);
}

.lesson-kicker {
  margin-bottom: 0.45rem;
  color: var(--red-dark);
  font-size: 0.75rem;
  font-weight: 800;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.lesson-card h3 {
  max-width: 54rem;
  margin-bottom: 1.25rem;
  font-family: Georgia, "Times New Roman", "Yu Mincho", serif;
  font-size: clamp(1.25rem, 2.6vw, 1.85rem);
  font-weight: 700;
  line-height: 1.35;
  overflow-wrap: anywhere;
}

.lesson-explanation {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1rem;
}

.lesson-section {
  min-width: 0;
  padding: 1rem 1.15rem;
  border: 1px solid var(--line);
  border-radius: 0.8rem;
  background: #fbf7ef;
}

.lesson-section.application {
  border-color: #b9d4cc;
  background: var(--teal-soft);
}

.lesson-section h4 {
  margin-bottom: 0.5rem;
  color: var(--ink);
  font-size: 0.9rem;
  line-height: 1.45;
}

.lesson-section p {
  margin-bottom: 0;
  color: var(--ink-soft);
  overflow-wrap: anywhere;
}

.lesson-official-link {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  max-width: 100%;
  margin-top: 1.15rem;
  padding-bottom: 0.1rem;
  color: var(--teal-dark);
  font-size: 0.9rem;
  font-weight: 800;
  overflow-wrap: anywhere;
  text-decoration: none;
  border-bottom: 2px solid var(--teal);
}

.lesson-official-link:hover {
  color: var(--red-dark);
  border-color: var(--red);
}

.course-nav {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 1rem 2rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--line);
}

.course-nav a {
  padding-bottom: 0.1rem;
  border-bottom: 2px solid var(--teal);
}

footer {
  padding: 1.75rem 0 3rem;
  border-top: 1px solid var(--line);
  color: var(--ink-soft);
  font-size: 0.8rem;
}

footer p {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 0.75rem 2rem;
  margin: 0;
}

@media (max-width: 60rem) {
  .hero {
    grid-template-columns: minmax(0, 1fr);
    gap: 2.5rem;
  }

  .hero-summary {
    max-width: 30rem;
  }

  .section-heading {
    grid-template-columns: minmax(0, 1fr);
    gap: 0.8rem;
  }
}

@media (max-width: 38rem) {
  .site-header {
    padding-top: 1rem;
    padding-bottom: 3.5rem;
  }

  .masthead {
    align-items: flex-start;
    flex-direction: column;
    gap: 0.6rem;
    padding-bottom: 2.25rem;
  }

  .hero {
    padding-top: 2.75rem;
  }

  h1 {
    max-width: 14ch;
    font-size: clamp(2.25rem, 12vw, 3.35rem);
  }

  .course-facts,
  .lesson-explanation {
    grid-template-columns: minmax(0, 1fr);
  }

  .lesson-card {
    grid-template-columns: 3.8rem minmax(0, 1fr);
    border-radius: 1rem;
  }

  .lesson-number {
    padding: 1.15rem 0.25rem;
    font-size: 2.25rem;
  }

  .lesson-body {
    padding: 1.15rem 1rem 1.35rem;
  }

  .lesson-card h3 {
    font-size: 1.2rem;
  }

  .course-nav {
    display: grid;
  }

  footer p {
    display: block;
  }

  footer p span {
    display: block;
  }

  footer p span + span {
    margin-top: 0.5rem;
  }
}

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