:root {
  --ink: #f7f3e8;
  --muted: rgba(247,243,232,.82);
  --soft: rgba(247,243,232,.58);
  --chalk: #fff8e6;
  --gold: #efe1a6;
  --panel: rgba(8, 11, 10, .52);
  --panel-strong: rgba(8, 11, 10, .76);
  --line: rgba(247,243,232,.34);
  --line-soft: rgba(247,243,232,.16);
  --shadow: 0 34px 100px rgba(0,0,0,.58);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: ui-rounded, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background: #050706;
  color: var(--ink);
  line-height: 1.6;
}
body.lang-ja { font-family: system-ui, -apple-system, BlinkMacSystemFont, "Hiragino Sans", "Yu Gothic", sans-serif; }
a { color: inherit; }

.page-bg {
  position: fixed;
  inset: 0;
  z-index: -2;
  background:
    linear-gradient(180deg, rgba(0,0,0,.18), rgba(0,0,0,.74)),
    url("../images/chalkboard-background-desktop.jpg") center/cover no-repeat;
}
.page-bg::after {
  content: "";
  position: absolute;
  inset: 0;
  background:
    radial-gradient(circle at 52% 18%, rgba(255,248,230,.08), transparent 28rem),
    radial-gradient(circle at 12% 16%, rgba(239,225,166,.07), transparent 24rem),
    rgba(0,0,0,.18);
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  gap: 1.4rem;
  padding: 1rem clamp(1rem, 4vw, 4.5rem);
  background: rgba(5, 7, 6, .72);
  backdrop-filter: blur(18px);
  border-bottom: 1px solid rgba(247,243,232,.16);
}
.brand { display:flex; align-items:center; gap:1rem; text-decoration:none; font-weight:900; letter-spacing:.12em; text-transform:uppercase; }
.brand-mark { width: clamp(5.3rem, 9vw, 8.5rem); height:auto; filter: drop-shadow(0 8px 16px rgba(0,0,0,.35)); }
.brand-name { white-space: nowrap; font-size: 1rem; }
.nav { display:flex; gap: clamp(.8rem, 2vw, 1.35rem); margin-left:auto; font-size:.95rem; }
.nav a { text-decoration:none; color:var(--muted); font-weight:760; }
.nav a:hover { color:var(--chalk); }
.language-picker select {
  border:1px solid var(--line);
  border-radius:999px;
  padding:.55rem .85rem;
  background:rgba(0,0,0,.44);
  color:var(--ink);
  font-weight:760;
}
.language-picker option { color: #111; }

.section, .section-grid { padding: clamp(4rem, 8vw, 7rem) clamp(1.15rem, 5vw, 6rem); max-width: 1420px; margin: 0 auto; }
.section-grid { display:grid; grid-template-columns: minmax(0, .98fr) minmax(330px, .82fr); gap: clamp(2rem, 6vw, 6rem); align-items:center; }
.hero { min-height: calc(100svh - 5rem); padding-top: clamp(2.5rem, 6vw, 5rem); padding-bottom: clamp(3rem, 6vw, 5rem); position:relative; }
.hero::after, .intro::before {
  content:"";
  position:absolute;
  left:clamp(1.2rem, 5vw, 6rem);
  right:clamp(1.2rem, 5vw, 6rem);
  bottom:0;
  height:1px;
  background:linear-gradient(90deg, transparent, rgba(247,243,232,.42), transparent);
}
.hero-logo { width:min(26rem, 70vw); height:auto; margin-bottom: clamp(1rem, 3vw, 2rem); filter: drop-shadow(0 10px 28px rgba(0,0,0,.42)); }
.eyebrow { color: var(--gold); font-size: .82rem; font-weight: 950; letter-spacing: .16em; text-transform: uppercase; margin: 0 0 .9rem; }
h1, h2, h3 { line-height:1.06; margin:0; color: var(--chalk); text-wrap: balance; }
h1 { font-size: clamp(4.6rem, 12vw, 8.8rem); letter-spacing: -.075em; text-shadow: 0 0 1px rgba(255,255,255,.75), 0 18px 44px rgba(0,0,0,.55); }
h1 span { color: var(--chalk); }
h2 { font-size: clamp(2.05rem, 4.8vw, 4.2rem); letter-spacing: -.045em; max-width: 15ch; }
h3 { font-size: 1.35rem; letter-spacing: -.018em; }
p { font-size: 1.08rem; color: var(--muted); }
.hero-lede { font-size: clamp(1.1rem, 1.8vw, 1.35rem); max-width: 42rem; }
.platforms { display:flex; flex-wrap:wrap; gap:1rem 1.7rem; margin:2rem 0 1.55rem; color:var(--ink); font-weight:760; }
.platforms > span { display:inline-flex; align-items:center; gap:.42rem; color:var(--muted); }
.platforms > span::first-letter { color:var(--chalk); }
.hero-actions { display:flex; flex-wrap:wrap; align-items:center; gap:1rem; margin-top:1rem; }
.app-store-badge { display:inline-flex; align-items:center; width: min(16rem, 70vw); transition: transform .18s ease, filter .18s ease; }
.app-store-badge img { width:100%; height:auto; display:block; filter: drop-shadow(0 14px 30px rgba(0,0,0,.45)); }
.app-store-badge:hover { transform: translateY(-2px); filter: brightness(1.08); }
.button { display:inline-flex; align-items:center; justify-content:center; min-height:3.1rem; padding:.78rem 1.18rem; border-radius:999px; text-decoration:none; font-weight:900; border:1px solid var(--line); }
.button.secondary { background:rgba(0,0,0,.22); color:var(--chalk); }
.button.secondary:hover { background:rgba(247,243,232,.1); }

.hero-art { position:relative; min-height: 38rem; display:grid; place-items:center; }
.phone-shot { width:min(25rem, 78vw); height:auto; transform: rotate(5deg); filter: drop-shadow(0 36px 56px rgba(0,0,0,.72)); }
.chalk-note { position:absolute; left:0; bottom:8%; transform:rotate(-8deg); color:var(--soft); font-size:1.1rem; font-weight:700; }

.intro { position:relative; }
.section-title.centered { text-align:center; max-width:860px; margin:0 auto 3rem; }
.section-title.centered h2 { margin:0 auto; max-width: 16ch; color:var(--gold); }
.section-title.centered p:last-child { max-width:780px; margin:1.2rem auto 0; }
.feature-row { display:grid; grid-template-columns: repeat(5, minmax(0,1fr)); gap:0; }
.feature-item { text-align:center; padding: 1rem clamp(.8rem, 2vw, 1.4rem); border-right:1px dashed rgba(247,243,232,.34); }
.feature-item:last-child { border-right:0; }
.feature-item img { width:5.3rem; height:5.3rem; opacity:.84; filter: drop-shadow(0 8px 18px rgba(0,0,0,.45)); margin-bottom:.65rem; }
.feature-item h3 { color: var(--gold); font-size:1.25rem; }
.feature-item p { font-size: .98rem; margin:.65rem auto 0; max-width:13rem; }

.chalk-panel, .card, .challenge-panel {
  background: var(--panel);
  border:1px solid var(--line-soft);
  box-shadow: 0 22px 70px rgba(0,0,0,.32);
  backdrop-filter: blur(10px);
}
.chalk-panel { border-radius: 2rem; }
.cards { display:grid; grid-template-columns: repeat(4, minmax(0,1fr)); gap:1rem; }
.section-heading { grid-column: 1 / -1; }
.section-heading h2 { color:var(--gold); }
.card { padding:1.45rem; border-radius:1.5rem; background:rgba(6,8,7,.48); }
.card h3 { color: var(--chalk); }
.card p { font-size:1rem; margin-bottom:0; }
.split { display:grid; grid-template-columns: 1fr 1fr; gap: clamp(2rem, 6vw, 5rem); align-items:center; }
.feature-list { list-style:none; padding:0; margin:0; display:grid; gap:.85rem; }
.feature-list li, .challenge-list span { background:rgba(247,243,232,.08); border:1px solid var(--line-soft); border-radius:1rem; padding:1rem 1.1rem; font-weight:820; color:var(--chalk); }
.challenge-panel { border-radius:2rem; background:rgba(35,43,38,.54); }
.challenge-list { display:grid; grid-template-columns: repeat(2,1fr); gap:.8rem; }
.challenge-list span { color:var(--gold); text-align:center; }
.download { text-align:center; }
.download h2 { margin:0 auto; max-width: 20ch; color:var(--gold); }
.download-logo { width:min(17rem, 80vw); margin-bottom:1rem; filter: drop-shadow(0 14px 28px rgba(0,0,0,.46)); }
.app-store-badge.large { margin-top:1rem; width:min(18rem, 76vw); }
.footer { display:flex; justify-content:space-between; align-items:center; padding:2rem clamp(1.2rem, 5vw, 6rem); border-top:1px solid var(--line-soft); color:var(--muted); background: rgba(3,5,4,.72); }
.footer p { margin:0; font-size:.95rem; }
.footer a { color:var(--chalk); font-weight:850; }
.sr-only { position:absolute; width:1px; height:1px; padding:0; margin:-1px; overflow:hidden; clip:rect(0,0,0,0); white-space:nowrap; border:0; }

@media (max-width: 1050px) {
  .site-header { flex-wrap:wrap; }
  .nav { order:3; width:100%; overflow:auto; margin-left:0; padding-bottom:.2rem; }
  .section-grid, .split { grid-template-columns:1fr; }
  .hero-art { min-height: auto; }
  .phone-shot { width:min(22rem, 76vw); }
  .feature-row { grid-template-columns: repeat(2, minmax(0,1fr)); gap:1.2rem; }
  .feature-item { border-right:0; border-bottom:1px dashed rgba(247,243,232,.26); }
  .cards { grid-template-columns: repeat(2, minmax(0,1fr)); }
}
@media (max-width: 620px) {
  .page-bg { background-image: linear-gradient(180deg, rgba(0,0,0,.16), rgba(0,0,0,.78)), url("../images/chalkboard-background-mobile.jpg"); }
  .brand-name { display:none; }
  .brand-mark { width:7rem; }
  .language-picker { margin-left:auto; }
  .cards, .challenge-list, .feature-row { grid-template-columns:1fr; }
  h1 { font-size: clamp(3.6rem, 17vw, 5.3rem); }
  .hero-logo { width:min(22rem, 82vw); }
  .hero-actions .button { width:100%; }
  .app-store-badge { width: min(17rem, 85vw); }
  .chalk-note { display:none; }
  .footer { flex-direction:column; gap:.7rem; }
}

.footer-links {
  display: flex;
  gap: 1.25rem;
  align-items: center;
  flex-wrap: wrap;
}

.footer-links a {
  color: var(--muted);
  text-decoration: none;
}

.footer-links a:hover {
  color: var(--chalk);
}