:root {
  --header-h: 64px;
  --logo-size: 60px;

  /* === Color Theme (Navy Light) === */
  --bg-main: #eef2f7;
  --bg-header: rgba(255, 255, 255, 0.82);

  --text-main: #0f172a;
  --text-sub: #334155;
  --text-muted: #64748b;

  --navy-accent: #1e3a8a;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--bg-main);
  color: var(--text-main);
  font-family: system-ui, -apple-system, BlinkMacSystemFont, sans-serif;
}

#top {
  position: absolute;
  top: 0;
  left: 0;
}

/* ===== Header (fixed) ===== */
.header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--header-h);

  z-index: 300;
  transform: translateZ(0);
  will-change: transform;

  display: flex;
  align-items: center;
  justify-content: center;

  background: var(--bg-header);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
}

.header-inner {
  max-width: 720px;
  width: 100%;
  padding: 0 24px;

  display: flex;
  align-items: center;
  justify-content: space-between;
}

.header-left {
  display: flex;
  align-items: center;
  gap: 12px;
  min-width: 140px;
}

.header-title {
  font-size: 0.95rem;
  letter-spacing: 0.12em;
  color: var(--navy-accent);
  opacity: 0.85;
  white-space: nowrap;
}

.header-title-link {
  color: inherit;
  text-decoration: none;
  border-bottom: none;
  display: inline-block;
}

.header-title-link:hover .header-title {
  opacity: 0.95;
}

.header-nav {
  display: flex;
  gap: 18px;
}

.header-nav a {
  font-size: 0.85rem;
  letter-spacing: 0.18em;
  color: var(--text-sub);
  opacity: 0.8;
  border-bottom: 1px solid rgba(30, 58, 138, 0.2);
  text-decoration: none;
}

.header-nav a:hover {
  color: var(--navy-accent);
  opacity: 1;
}

/* ===== Layout ===== */
.wrapper {
  min-height: 100vh;
  display: flex;
  justify-content: center;
  padding: calc(120px + var(--header-h)) 24px 120px;
}

.content {
  max-width: 720px;
  width: 100%;
}

h1 {
  font-size: 3.5rem;
  letter-spacing: 0.06em;
  margin: 0 0 1rem;
  text-align: center;
  color: var(--navy-accent);
}

.tagline {
  font-size: 1.1rem;
  letter-spacing: 0.08em;
  color: var(--text-muted);
  margin-bottom: 6rem;
  text-align: center;
}

section {
  max-width: 430px;
  margin: 0 auto 5rem;
  text-align: left;
}

h2 {
  font-size: 0.75rem;
  letter-spacing: 0.25em;
  color: var(--text-muted);
  margin-bottom: 1.2rem;
}

p {
  line-height: 2;
  font-size: 1rem;
  color: var(--text-sub);
  margin: 0;
}

ul {
  list-style: none;
  padding: 0;
  margin: 0;
}

footer {
  max-width: 430px;
  margin: 6rem auto 0;
  text-align: left;
  font-size: 0.85rem;
  opacity: 0.5;
}

a {
  color: var(--navy-accent);
  text-decoration: none;
  border-bottom: 1px solid rgba(30, 58, 138, 0.25);
}

a:hover {
  border-bottom-color: rgba(30, 58, 138, 0.6);
}

/* ===== Hero ===== */
.hero {
  text-align: center;
  margin-bottom: 6rem;
}

/* ===== PC: reduce vertical spacing ===== */
@media (min-width: 768px) {
  .wrapper {
    padding: calc(60px + var(--header-h)) 24px 60px;
  }

  .tagline {
    margin-bottom: 3rem;
  }

  .hero {
    margin-bottom: 3rem;
  }

  section {
    margin-bottom: 2.5rem;
  }

  footer {
    margin-top: 3rem;
  }
}

.logo-spacer {
  height: var(--logo-size);
  margin: 0 auto 1.2rem;
}

.logo-fixed {
  width: var(--logo-size);
  opacity: 1;

  position: fixed;
  left: 50%;

  transform: translateX(-50%) translateZ(0);
  isolation: isolate;
  z-index: 1000;

  top: 0;

  transition: opacity 180ms ease;
  will-change: top, opacity;
  pointer-events: none;
}

.logo-fixed.is-stuck {
  opacity: 0.7;
}