:root {
  --palette-paper: #f5efe2;
  --palette-surface: #fffdf8;
  --palette-navy: #1c2b45;
  --palette-navy-deep: #0f1e35;
  --palette-gold: #7d5e26;
  --palette-gold-soft: #efe4c8;
  --palette-ink: #33312c;
  --palette-muted: #645e50;
  --palette-line: #e2d8bf;
  --palette-red: #a34848;
  --color-bg-page: var(--palette-paper);
  --color-bg-surface: var(--palette-surface);
  --color-text-primary: var(--palette-ink);
  --color-text-secondary: var(--palette-muted);
  --color-text-inverse: var(--palette-surface);
  --color-brand: var(--palette-navy);
  --color-brand-strong: var(--palette-navy-deep);
  --color-accent: var(--palette-gold);
  --color-accent-soft: var(--palette-gold-soft);
  --color-border: var(--palette-line);
  --color-status-warning: var(--palette-red);
  --color-link: var(--palette-navy);
  --color-button-primary-bg: var(--palette-navy);
  --color-button-primary-fg: var(--palette-surface);
  --font-serif: "Hiragino Mincho ProN", "Yu Mincho", "Noto Serif JP", serif;
  --font-sans: -apple-system, BlinkMacSystemFont, "Hiragino Kaku Gothic ProN", "Yu Gothic", "Noto Sans JP", sans-serif;
}

*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--color-text-primary);
  background:
    radial-gradient(circle at 18% 2%, rgba(125, 94, 38, .06), transparent 24rem),
    var(--color-bg-page);
  font: 16px/1.9 var(--font-sans);
  letter-spacing: .02em;
}
img { display: block; max-width: 100%; height: auto; }
a { color: var(--color-link); text-underline-offset: .22em; }
a:focus-visible, summary:focus-visible {
  outline: 3px solid var(--color-status-warning);
  outline-offset: 3px;
  border-radius: 4px;
}
h1, h2, h3, p { margin-top: 0; }
h1, h2, h3 { color: var(--color-brand); font-family: var(--font-serif); font-weight: 600; }

.learn-site-header {
  position: sticky;
  top: 0;
  z-index: 30;
  min-height: 64px;
  background: var(--color-bg-surface);
  border-bottom: 1px solid var(--color-border);
}
.learn-site-header__inner {
  width: min(1120px, calc(100% - 48px));
  min-height: 64px;
  margin-inline: auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 28px;
}
.learn-site-header__brand {
  color: var(--color-brand);
  font: 600 1.22rem/1 var(--font-serif);
  letter-spacing: .08em;
  text-decoration: none;
}
.learn-site-header__nav { display: flex; align-items: center; gap: 26px; }
.learn-site-header__nav > a:not(.learn-primary-link) { color: var(--color-text-secondary); font-size: .86rem; text-decoration: none; }
.learn-primary-link {
  min-height: 42px;
  padding: 9px 18px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  color: var(--color-button-primary-fg);
  background: var(--color-button-primary-bg);
  border: 1px solid var(--color-brand);
  border-radius: 4px;
  font-size: .82rem;
  font-weight: 700;
  text-decoration: none;
}
.learn-mobile-menu { display: none; position: relative; }
.learn-mobile-menu summary { min-width: 44px; min-height: 44px; display: grid; place-items: center; color: var(--color-brand); cursor: pointer; font-size: 0; list-style: none; }
.learn-mobile-menu summary::-webkit-details-marker { display: none; }
.learn-mobile-menu summary::before { content: "☰"; font: 1.35rem/1 var(--font-sans); }
.learn-mobile-menu[open] summary::before { content: "×"; }
.learn-mobile-menu__panel {
  position: absolute;
  top: calc(100% + 7px);
  right: 0;
  width: min(19rem, calc(100vw - 32px));
  padding: 12px;
  display: grid;
  gap: 8px;
  background: var(--color-bg-surface);
  border: 1px solid var(--color-border);
  box-shadow: 0 14px 30px rgba(15, 30, 53, .12);
}
.learn-mobile-menu__panel a { min-height: 44px; padding: 9px 12px; display: flex; align-items: center; text-decoration: none; }
.learn-mobile-menu__panel .learn-primary-link { justify-content: center; color: var(--color-button-primary-fg); }

.learn-container { width: min(1120px, calc(100% - 48px)); margin-inline: auto; }
.learn-breadcrumb { padding-block: 20px 10px; color: var(--color-text-secondary); font-size: .78rem; }
.learn-breadcrumb ol { margin: 0; padding: 0; display: flex; flex-wrap: wrap; gap: 7px; list-style: none; }
.learn-breadcrumb li:not(:last-child)::after { content: ">"; margin-left: 7px; color: var(--color-border); }
.learn-breadcrumb a { color: inherit; }

.learn-overline { margin-bottom: 8px; color: var(--color-accent); font-size: .76rem; font-weight: 700; letter-spacing: .18em; }
.learn-index-hero { padding: 52px 0 42px; border-bottom: 1px solid var(--color-border); }
.learn-index-hero__grid { display: grid; grid-template-columns: minmax(0, 1.35fr) minmax(240px, .65fr); gap: 64px; align-items: center; }
.learn-index-hero h1 { margin-bottom: 14px; font-size: clamp(2.1rem, 4vw, 3.2rem); line-height: 1.35; letter-spacing: .08em; }
.learn-index-hero__lead { max-width: 36rem; color: var(--color-text-secondary); }
.learn-index-action { min-height: 52px; margin-top: 24px; padding: 12px 24px; display: inline-flex; align-items: center; color: var(--color-text-inverse); background: var(--color-brand); border-radius: 4px; font-weight: 700; text-decoration: none; }
.learn-index-progress { padding: 24px; background: var(--color-bg-surface); border: 1px solid var(--color-border); border-radius: 5px; }
.learn-index-progress > span { display: block; margin-bottom: 7px; color: var(--color-text-secondary); font-size: .78rem; }
.learn-index-progress strong { color: var(--color-brand); font: 600 2.1rem/1.2 var(--font-serif); }
.learn-index-progress strong small { font: 400 .9rem/1 var(--font-sans); }
.learn-progress { height: 7px; margin-top: 16px; overflow: hidden; background: var(--color-border); border-radius: 99px; }
.learn-progress__bar { width: var(--progress); height: 100%; background: var(--color-accent); }

.learn-chapter-nav { padding: 18px 0; border-bottom: 1px solid var(--color-border); }
.learn-chapter-nav__inner { display: flex; gap: 8px; overflow-x: auto; scrollbar-width: thin; }
.learn-chapter-nav a { flex: 0 0 auto; padding: 7px 12px; color: var(--color-text-secondary); border: 1px solid var(--color-border); background: var(--color-bg-surface); text-decoration: none; font-size: .8rem; }

.learn-chapters { padding: 34px 0 68px; }
.learn-chapter { margin-bottom: 16px; background: var(--color-bg-surface); border: 1px solid var(--color-border); border-radius: 5px; }
.learn-chapter > summary { min-height: 62px; padding: 14px 18px; display: grid; grid-template-columns: 7rem 1fr auto; gap: 16px; align-items: center; cursor: pointer; list-style: none; }
.learn-chapter > summary::-webkit-details-marker { display: none; }
.learn-chapter > summary::after { content: "⌄"; color: var(--color-accent); }
.learn-chapter[open] > summary::after { content: "⌃"; }
.learn-chapter__label { color: var(--color-accent); font-size: .79rem; font-weight: 700; }
.learn-chapter__title { margin: 0; color: var(--color-brand); font: 600 1.04rem/1.5 var(--font-serif); }
.learn-chapter__range { color: var(--color-text-secondary); font-size: .75rem; white-space: nowrap; }
.learn-chapter__body { border-top: 1px solid var(--color-border); }
.learn-lesson-list { margin: 0; padding: 0; list-style: none; }
.learn-lesson { min-height: 50px; border-top: 1px solid rgba(226, 216, 191, .62); }
.learn-lesson:first-child { border-top: 0; }
.learn-lesson > a, .learn-lesson > div { min-height: 50px; padding: 10px 18px; display: grid; grid-template-columns: 3rem 1fr 7rem; gap: 12px; align-items: center; }
.learn-lesson > a { text-decoration: none; }
.learn-lesson > a:hover .learn-lesson__title { text-decoration: underline; }
.learn-lesson__number { color: var(--color-brand); font-size: .78rem; font-variant-numeric: tabular-nums; }
.learn-lesson__title { min-width: 0; color: var(--color-text-primary); font-size: .88rem; }
.learn-lesson__status { justify-self: end; color: var(--color-accent); font-size: .76rem; text-align: right; }
.learn-lesson--planned .learn-lesson__title, .learn-lesson--planned .learn-lesson__status { color: var(--color-text-secondary); }
.learn-zero-note { margin: 28px 0 0; color: var(--color-text-secondary); font-size: .84rem; text-align: center; }

.learn-site-footer { padding: 34px 24px; color: var(--color-text-inverse); background: var(--color-brand-strong); font-size: .79rem; text-align: center; }
.learn-site-footer__nav { margin-bottom: 12px; display: flex; justify-content: center; flex-wrap: wrap; gap: 8px 22px; }
.learn-site-footer a { color: var(--color-text-inverse); }

.learn-article { padding-bottom: 72px; }
.learn-article__course { padding: 13px 0; display: grid; grid-template-columns: 1fr auto minmax(160px, 300px); gap: 18px; align-items: center; border-block: 1px solid var(--color-border); color: var(--color-text-secondary); font-size: .8rem; }
.learn-article__course strong { color: var(--color-brand); }
.learn-article__header { width: min(760px, 100%); margin-top: 38px; }
.learn-article__grid { margin-top: 38px; display: grid; grid-template-columns: minmax(0, 760px) 260px; gap: 64px; align-items: start; }
.learn-article__main { min-width: 0; }
.learn-article__header h1 { margin-bottom: 24px; font-size: clamp(2rem, 4vw, 2.75rem); line-height: 1.45; letter-spacing: .06em; }
.learn-outcomes { margin-bottom: 18px; padding: 20px 22px; background: rgba(239, 228, 200, .45); border: 1px solid var(--color-accent); border-radius: 5px; }
.learn-outcomes h2 { margin-bottom: 10px; font: 600 1rem/1.5 var(--font-serif); }
.learn-outcomes ul { margin: 0; padding: 0; display: grid; gap: 5px; list-style: none; }
.learn-outcomes li { position: relative; padding-left: 24px; font-size: .88rem; }
.learn-outcomes li::before { content: "✓"; position: absolute; left: 0; color: var(--color-accent); font-weight: 700; }
.learn-article__meta { margin-bottom: 34px; display: flex; flex-wrap: wrap; gap: 6px 20px; color: var(--color-text-secondary); font-size: .76rem; }
.learn-article__meta dl { margin: 0; display: contents; }
.learn-article__meta div { display: flex; gap: 5px; }
.learn-article__meta dt { color: var(--color-text-secondary); }
.learn-article__meta dd { margin: 0; color: var(--color-text-primary); }
.learn-article__toc { position: sticky; top: 88px; padding: 20px; background: var(--color-bg-surface); border: 1px solid var(--color-border); border-radius: 5px; }
.learn-article__toc summary { color: var(--color-brand); font: 600 1rem/1.5 var(--font-serif); cursor: pointer; }
.learn-article__toc ol { margin: 14px 0 0; padding-left: 1.25rem; }
.learn-article__toc li { margin-top: 8px; color: var(--color-text-secondary); font-size: .78rem; }
.learn-article__toc a { color: inherit; text-decoration: none; }
.learn-article__toc a:hover { text-decoration: underline; }

.article-body { color: var(--color-text-primary); font-size: clamp(1rem, .97rem + .15vw, 1.075rem); line-height: 1.95; letter-spacing: .02em; }
.article-body p { margin: 0 0 1.7em; }
.article-body h2 { margin: 3.5em 0 1.2em; font-size: clamp(1.45rem, 1.25rem + .7vw, 1.9rem); line-height: 1.5; scroll-margin-top: 96px; }
.article-body h3 { margin: 2.5em 0 .9em; font: 600 1.2rem/1.6 var(--font-sans); scroll-margin-top: 96px; }
.article-body ul, .article-body ol { margin: 0 0 1.7em; padding-left: 1.4em; }
.article-body blockquote { margin: 2em 0; padding: 1em 1.2em; color: var(--color-text-secondary); background: var(--color-accent-soft); border-left: 3px solid var(--color-accent); }
.article-figure { margin: 42px 0; }
.article-figure img { width: 100%; border: 1px solid var(--color-border); }
.article-figure figcaption { margin-top: 8px; color: var(--color-text-secondary); font-size: .76rem; text-align: center; }
.article-table { margin: 32px 0; overflow-x: auto; }
.article-table table { width: 100%; border-collapse: collapse; background: var(--color-bg-surface); }
.article-table th, .article-table td { padding: 10px 12px; border-bottom: 1px solid var(--color-border); text-align: left; }

.learn-summary { margin-top: 52px; padding: 22px; background: rgba(239, 228, 200, .45); border: 1px solid var(--color-accent); border-radius: 5px; }
.learn-summary h2 { margin-bottom: 10px; font: 600 1.05rem/1.5 var(--font-serif); }
.learn-summary ul { margin: 0; padding-left: 1.3rem; }
.learn-lesson-nav { margin-top: 22px; display: grid; grid-template-columns: 1fr 1fr; gap: 14px; }
.learn-lesson-nav a, .learn-lesson-nav span { min-height: 96px; padding: 16px 18px; display: flex; flex-direction: column; justify-content: center; border: 1px solid var(--color-border); background: var(--color-bg-surface); text-decoration: none; }
.learn-lesson-nav small { margin-bottom: 4px; color: var(--color-text-secondary); }
.learn-lesson-nav strong { color: var(--color-brand); font: 600 1rem/1.6 var(--font-serif); }
.learn-lesson-nav__next { color: var(--color-text-inverse) !important; background: var(--color-accent) !important; border-color: var(--color-accent) !important; text-align: right; }
.learn-lesson-nav__next small, .learn-lesson-nav__next strong { color: var(--color-text-inverse); }
.learn-article__end-progress { margin-top: 20px; padding: 14px 0; display: grid; grid-template-columns: auto 1fr; gap: 18px; align-items: center; color: var(--color-text-secondary); font-size: .8rem; }
.learn-article__end-progress .learn-progress { margin-top: 0; }
.learn-operator { margin-top: 30px; padding: 20px; display: grid; grid-template-columns: 68px 1fr; gap: 16px; align-items: center; background: var(--color-bg-surface); border: 1px solid var(--color-border); }
.learn-operator img { width: 68px; height: 68px; border-radius: 50%; object-fit: cover; border: 1px solid var(--color-accent); }
.learn-operator h2 { margin-bottom: 4px; font: 600 1rem/1.5 var(--font-serif); }
.learn-operator p { margin: 0; color: var(--color-text-secondary); font-size: .8rem; }
.learn-next-actions { margin-top: 18px; }
.learn-next-actions h2 { margin-bottom: 10px; font: 600 .88rem/1.5 var(--font-sans); }
.learn-next-actions__grid { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; }
.learn-next-actions a { min-height: 88px; padding: 16px; display: flex; flex-direction: column; justify-content: center; color: var(--color-brand); background: var(--color-bg-surface); border: 1px solid var(--color-border); text-decoration: none; }
.learn-next-actions small { color: var(--color-text-secondary); }

@media (min-width: 701px) {
  .learn-chapter:not([open]) > .learn-chapter__body { display: block; }
  .learn-chapter > summary::after { display: none; }
}

@media (max-width: 860px) {
  .learn-site-header__inner, .learn-container { width: min(100% - 32px, 760px); }
  .learn-site-header__inner { min-height: 56px; }
  .learn-site-header { min-height: 56px; }
  .learn-site-header__nav { display: none; }
  .learn-mobile-menu { display: block; }
  .learn-index-hero { padding: 38px 0 30px; }
  .learn-index-hero__grid { grid-template-columns: 1fr; gap: 28px; }
  .learn-index-hero h1 { font-size: 2rem; }
  .learn-index-action { min-height: 48px; margin-top: 18px; }
  .learn-index-progress { padding: 18px; }
  .learn-chapter > summary { grid-template-columns: 4.5rem 1fr auto; gap: 9px; }
  .learn-chapter__range { grid-column: 2; }
  .learn-chapter > summary::after { grid-column: 3; grid-row: 1 / span 2; }
  .learn-lesson > a, .learn-lesson > div { grid-template-columns: 2.35rem minmax(0, 1fr) auto; padding-inline: 12px; }
  .learn-lesson__status { max-width: 5.5rem; }
  .learn-article__course { grid-template-columns: 1fr auto; gap: 8px 14px; }
  .learn-article__course .learn-progress { grid-column: 1 / -1; width: 100%; margin-top: 0; }
  .learn-article__header { margin-top: 28px; }
  .learn-article__grid { margin-top: 26px; display: flex; flex-direction: column; gap: 26px; }
  .learn-article__aside { width: 100%; order: -1; }
  .learn-article__toc { position: static; padding: 14px 16px; }
  .learn-article__header h1 { font-size: 1.85rem; }
}

@media (max-width: 540px) {
  .learn-chapter__title { font-size: .93rem; }
  .learn-lesson > a, .learn-lesson > div { grid-template-columns: 2.25rem minmax(0, 1fr); gap: 7px; }
  .learn-lesson__status { grid-column: 2; justify-self: start; max-width: none; }
  .learn-lesson-nav, .learn-next-actions__grid { grid-template-columns: 1fr; }
  .learn-lesson-nav__next { text-align: left; }
  .learn-article__end-progress { grid-template-columns: 1fr; gap: 8px; }
  .learn-operator { grid-template-columns: 54px 1fr; padding: 16px; }
  .learn-operator img { width: 54px; height: 54px; }
}

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

@media print {
  .learn-site-header, .learn-site-footer, .learn-article__aside, .learn-lesson-nav, .learn-next-actions { display: none !important; }
  body { background: var(--color-bg-surface); }
  .learn-container { width: 100%; }
  .learn-article__grid { display: block; }
}