@import url('https://fonts.googleapis.com/css2?family=Noto+Sans+JP:wght@300;400;500;700&family=Noto+Serif+JP:wght@400;500;600;700&display=swap');

:root {
  --ink: #000000;
  --paper: #ffffff;
  --hair: rgba(0, 0, 0, .18);
  --soft: #f2f2f2;
}

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

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: 'Noto Sans JP', system-ui, -apple-system, 'Hiragino Kaku Gothic ProN', sans-serif;
  font-size: 17px;
  font-weight: 400;
  line-height: 1.8;
  letter-spacing: .012em;
  overflow-x: hidden;
}

a { color: inherit; }

img { max-width: 100%; }

/* ---------- 顶栏 ---------- */

.masthead {
  position: sticky;
  top: 0;
  z-index: 40;
  background: var(--paper);
  border-bottom: 2px solid var(--ink);
}

.masthead__rail {
  max-width: 1200px;
  margin: 0 auto;
  padding: .4rem 1.25rem;
  min-height: 4.25rem;
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  gap: 1rem;
}

.rail__left { display: flex; justify-content: flex-start; }
.rail__right { display: flex; justify-content: flex-end; align-items: center; gap: .6rem; }

.brand {
  font-family: 'Noto Serif JP', serif;
  font-size: 1.2rem;
  font-weight: 700;
  letter-spacing: .2em;
  text-decoration: none;
  text-align: center;
  white-space: nowrap;
  padding: .45rem .2rem;
}

.drop { position: relative; }

.drop > summary {
  list-style: none;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: .5rem;
  min-height: 44px;
  padding: .5rem .75rem;
  font-size: .92rem;
  letter-spacing: .14em;
  border: 1px solid transparent;
  transition: border-color .2s ease;
}

.drop > summary::-webkit-details-marker { display: none; }

.drop > summary::after {
  content: "";
  width: .45em;
  height: .45em;
  border-right: 1.5px solid var(--ink);
  border-bottom: 1.5px solid var(--ink);
  transform: rotate(45deg) translateY(-2px);
  transition: transform .2s ease;
}

.drop[open] > summary { border-color: var(--ink); }
.drop[open] > summary::after { transform: rotate(-135deg) translateY(-2px); }

.drop menu {
  position: absolute;
  top: calc(100% + .5rem);
  left: 0;
  z-index: 45;
  margin: 0;
  padding: .25rem 0;
  min-width: 12rem;
  list-style: none;
  background: var(--paper);
  border: 2px solid var(--ink);
}

.rail__right .drop menu { left: auto; right: 0; }

.drop menu li a {
  display: flex;
  align-items: center;
  min-height: 44px;
  padding: .35rem 1rem;
  text-decoration: none;
  font-size: .92rem;
  letter-spacing: .06em;
  border-bottom: 1px solid var(--hair);
  transition: background-color .2s ease, color .2s ease;
}

.drop menu li:last-child a { border-bottom: 0; }
.drop menu li a:hover { background: var(--ink); color: var(--paper); }

.cta {
  display: inline-flex;
  align-items: center;
  min-height: 44px;
  padding: .5rem 1.1rem;
  background: var(--ink);
  color: var(--paper);
  border: 2px solid var(--ink);
  text-decoration: none;
  font-size: .88rem;
  letter-spacing: .12em;
  transition: background-color .22s ease, color .22s ease;
}

.cta:hover { background: var(--paper); color: var(--ink); }

/* ---------- 首屏 ---------- */

.hero {
  position: relative;
  max-width: 1200px;
  margin: 0 auto;
  min-height: 45vh;
  padding: 2.75rem 1.25rem;
  display: grid;
  place-items: center;
  overflow: hidden;
}

.hero__plate {
  position: absolute;
  z-index: 0;
  overflow: hidden;
  background: var(--soft);
  transition: width .7s ease, top .7s ease, right .7s ease, bottom .7s ease, left .7s ease;
}

.hero__plate--a {
  top: 1.25rem;
  left: 0;
  width: 34%;
  max-width: 300px;
  aspect-ratio: 5 / 4;
  animation: driftA 11s ease-in-out infinite alternate;
}

.hero__plate--b {
  bottom: 1.25rem;
  right: 0;
  width: 26%;
  max-width: 230px;
  aspect-ratio: 3 / 4;
  animation: driftB 14s ease-in-out infinite alternate;
}

.hero__pic {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: cover;
  filter: grayscale(1) contrast(1.06);
}

@keyframes driftA {
  from { transform: translate3d(0, -8px, 0); }
  to   { transform: translate3d(0, 12px, 0); }
}

@keyframes driftB {
  from { transform: translate3d(0, 10px, 0); }
  to   { transform: translate3d(0, -10px, 0); }
}

.hero__copy {
  position: relative;
  z-index: 1;
  max-width: 32rem;
  padding: 0 .5rem;
  text-align: center;
}

.hero__badge {
  display: inline-block;
  padding: .35rem .8rem .35rem 1rem;
  background: var(--ink);
  color: var(--paper);
  font-size: .7rem;
  letter-spacing: .3em;
}

.hero__title {
  font-family: 'Noto Serif JP', serif;
  font-size: clamp(1.9rem, 6vw, 3.4rem);
  font-weight: 700;
  line-height: 1.32;
  letter-spacing: .05em;
  margin: 1.1rem 0 1.2rem;
}

.hero__lede {
  margin: 0 auto;
  max-width: 28rem;
  font-size: .95rem;
  line-height: 1.95;
  letter-spacing: .05em;
}

/* ---------- 主体 ---------- */

main {
  max-width: 1200px;
  margin: 0 auto;
  padding: 2.5rem 1.25rem 4.5rem;
  border-top: 2px solid var(--ink);
  display: grid;
  grid-template-columns: minmax(0, 1fr) 19rem;
  gap: 3.5rem;
  align-items: start;
}

main > section { min-width: 0; }

main section > div {
  border-top: 1px solid var(--ink);
  margin-top: 3rem;
  padding-top: 2.25rem;
  scroll-margin-top: 6.5rem;
}

main section > div:first-child {
  border-top: 0;
  margin-top: 0;
  padding-top: 0;
}

main section h2 {
  font-family: 'Noto Serif JP', serif;
  font-size: clamp(1.45rem, 3.2vw, 2.05rem);
  font-weight: 700;
  line-height: 1.45;
  letter-spacing: .03em;
  margin: 0 0 1rem;
}

main section h3 {
  font-size: 1.14rem;
  font-weight: 700;
  letter-spacing: .03em;
  margin: 2rem 0 .6rem;
}

main section p {
  margin: 0 0 1.15rem;
  max-width: 42rem;
}

main section ul,
main section ol {
  margin: 0 0 1.25rem;
  padding-left: 1.35rem;
  max-width: 42rem;
}

main section li { margin: .35rem 0; }

main section a {
  text-decoration: underline;
  text-underline-offset: .22em;
}

main section blockquote {
  margin: 1.5rem 0;
  padding: .25rem 0 .25rem 1.1rem;
  border-left: 3px solid var(--ink);
  font-family: 'Noto Serif JP', serif;
}

main section blockquote p:last-child { margin-bottom: 0; }

main section code {
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: .92em;
  background: var(--soft);
  padding: .1em .35em;
}

/* ---------- 侧栏 ---------- */

.side {
  position: sticky;
  top: 6.5rem;
  border-top: 3px solid var(--ink);
  padding-top: .85rem;
}

.side__kick {
  display: block;
  font-size: .7rem;
  letter-spacing: .3em;
  margin: 0 0 .4rem;
}

.side__title {
  font-family: 'Noto Serif JP', serif;
  font-size: 1.02rem;
  font-weight: 700;
  letter-spacing: .12em;
  margin: 0 0 1rem;
}

.side__list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.side__list li a {
  display: flex;
  align-items: center;
  min-height: 44px;
  padding: .55rem 0;
  font-size: .92rem;
  letter-spacing: .05em;
  text-decoration: none;
  border-bottom: 1px solid var(--hair);
  transition: padding-left .2s ease, border-color .2s ease;
}

.side__list li a:hover {
  padding-left: .55rem;
  border-bottom-color: var(--ink);
}

/* ---------- 页脚 ---------- */

.colophon {
  max-width: 1200px;
  margin: 0 auto;
  padding: 2.5rem 1.25rem 1.75rem;
  border-top: 2px solid var(--ink);
}

.colophon__lead {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 1rem 2rem;
  padding-bottom: 1.75rem;
  margin-bottom: 2.25rem;
  border-bottom: 1px solid var(--ink);
}

.colophon__big {
  margin: 0;
  font-family: 'Noto Serif JP', serif;
  font-size: clamp(1.4rem, 4.4vw, 2.3rem);
  font-weight: 700;
  letter-spacing: .1em;
  line-height: 1.3;
}

.colophon__jump {
  display: inline-flex;
  align-items: center;
  min-height: 44px;
  padding: .5rem 1.2rem;
  border: 2px solid var(--ink);
  text-decoration: none;
  font-size: .88rem;
  letter-spacing: .14em;
  transition: background-color .22s ease, color .22s ease;
}

.colophon__jump:hover { background: var(--ink); color: var(--paper); }

.colophon__grid {
  display: grid;
  grid-template-columns: 1fr 1.25fr;
  gap: 2.5rem;
}

.colophon__right {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 2.5rem;
}

.colophon__dl { margin: 0; }

.colophon__dl dt {
  font-size: .72rem;
  letter-spacing: .26em;
  padding-bottom: .45rem;
  margin-bottom: .5rem;
  border-bottom: 2px solid var(--ink);
}

.colophon__dl dd { margin: 0; }

.colophon__dl dd a {
  display: inline-flex;
  align-items: center;
  min-height: 40px;
  font-size: .9rem;
  letter-spacing: .05em;
  text-decoration: none;
}

.colophon__dl dd a:hover { text-decoration: underline; text-underline-offset: .2em; }

.colophon__cr {
  margin: 2.25rem 0 0;
  padding-top: 1rem;
  border-top: 1px solid var(--hair);
  font-size: .78rem;
  letter-spacing: .14em;
}

/* ---------- 断点 ---------- */

@media (max-width: 900px) {
  main {
    grid-template-columns: minmax(0, 1fr);
    gap: 0;
  }
  .side { position: static; margin-top: 3.5rem; }
  .colophon__grid { grid-template-columns: 1fr; }
}

@media (max-width: 620px) {
  body { font-size: 16px; }

  .masthead__rail {
    grid-template-columns: auto 1fr auto;
    gap: .35rem;
    padding: .3rem .7rem;
    min-height: 3.7rem;
  }

  .brand { font-size: .99rem; letter-spacing: .12em; }
  .rail__right .cta { display: none; }
  .drop > summary { padding: .5rem .5rem; letter-spacing: .1em; }

  .hero { padding: 2rem .9rem 3.25rem; min-height: 45vh; }
  .hero__plate { opacity: .45; }
  .hero__plate--a { width: 44%; top: .75rem; }
  .hero__plate--b { width: 34%; bottom: .75rem; }
  .hero__copy { padding: 0; }
  .hero__badge { font-size: .65rem; letter-spacing: .22em; }

  main { padding: 2rem .9rem 3.5rem; }
  main section p, main section ul, main section ol { max-width: 100%; }

  .colophon { padding: 2rem .9rem 1.5rem; }
  .colophon__right { grid-template-columns: 1fr 1fr; gap: 1.5rem; }
  .colophon__grid { gap: 1.75rem; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .hero__plate { animation: none; transition: none; }
  .drop menu li a,
  .cta,
  .side__list li a,
  .colophon__jump { transition: none; }
}

button[aria-expanded]{min-width:44px;min-height:44px}