:root {
  --color-primary: #0ea5e9;
  --color-primary-dark: #0369a1;
  --color-text: #0f172a;
  --color-text-soft: #475569;
  --color-bg: #f8fafc;
  --color-card: #ffffff;
  --color-border: #e2e8f0;
  --color-warning-bg: #fef3c7;
  --color-warning-border: #f59e0b;
  --shadow: 0 10px 30px rgba(15, 23, 42, 0.08);
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  font-family: "Yu Gothic", "Hiragino Kaku Gothic ProN", "Noto Sans JP", "Helvetica Neue", Arial, sans-serif;
  color: var(--color-text);
  background: var(--color-bg);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
}

.container {
  max-width: 880px;
  margin: 0 auto;
  padding: 0 24px;
}

/* Hero */
.hero {
  background: linear-gradient(135deg, #e0f2fe 0%, #f0f9ff 100%);
  padding: 64px 0 56px;
  text-align: center;
}

.eyebrow {
  color: var(--color-primary-dark);
  font-size: 14px;
  letter-spacing: 0.1em;
  margin: 0 0 8px;
  font-weight: 600;
}

.hero h1 {
  margin: 0 0 12px;
  font-size: 44px;
  letter-spacing: 0.02em;
  color: var(--color-text);
}

.tagline {
  color: var(--color-text-soft);
  font-size: 17px;
  margin: 0 0 40px;
}

/* Download card */
.download-card {
  background: var(--color-card);
  border-radius: 16px;
  padding: 32px 24px;
  max-width: 520px;
  margin: 0 auto;
  box-shadow: var(--shadow);
}

.version-label {
  margin: 0 0 16px;
  color: var(--color-text-soft);
  font-size: 14px;
}

.version-label span {
  color: var(--color-text);
  font-weight: 600;
}

.download-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
  background: var(--color-primary);
  color: #fff;
  text-decoration: none;
  padding: 18px 40px;
  border-radius: 12px;
  font-size: 18px;
  font-weight: 700;
  width: 100%;
  transition: background 0.15s, transform 0.05s;
  box-shadow: 0 4px 14px rgba(14, 165, 233, 0.3);
}

.download-btn:hover {
  background: var(--color-primary-dark);
}

.download-btn:active {
  transform: translateY(1px);
}

.download-btn .os-icon {
  font-size: 22px;
  font-weight: 400;
}

.download-btn .size {
  font-size: 13px;
  opacity: 0.85;
  font-weight: 400;
}

.sub-note {
  margin: 16px 0 0;
  font-size: 13px;
  color: var(--color-text-soft);
}

.fallback {
  margin: 16px 0 0;
  font-size: 13px;
  color: #b91c1c;
}

.fallback a { color: #b91c1c; }

/* Sections */
main section {
  padding: 56px 0;
}

main section + section {
  padding-top: 0;
}

main h2 {
  font-size: 26px;
  margin: 0 0 28px;
  text-align: center;
  color: var(--color-text);
}

main h2::after {
  content: "";
  display: block;
  width: 48px;
  height: 3px;
  background: var(--color-primary);
  margin: 12px auto 0;
  border-radius: 2px;
}

/* Steps */
.steps {
  list-style: none;
  padding: 0;
  margin: 0;
  display: grid;
  gap: 16px;
}

.steps li {
  display: flex;
  gap: 20px;
  background: var(--color-card);
  border: 1px solid var(--color-border);
  border-radius: 12px;
  padding: 24px;
}

.step-num {
  flex-shrink: 0;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: var(--color-primary);
  color: #fff;
  font-weight: 700;
  font-size: 20px;
  display: flex;
  align-items: center;
  justify-content: center;
}

.step-body h3 {
  margin: 0 0 6px;
  font-size: 18px;
}

.step-body p {
  margin: 0;
  color: var(--color-text-soft);
  font-size: 15px;
}

.step-body code {
  background: #f1f5f9;
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 13px;
}

/* Alert */
.alert-section { padding-top: 0 !important; }

.alert {
  background: var(--color-warning-bg);
  border-left: 6px solid var(--color-warning-border);
  border-radius: 8px;
  padding: 20px 24px;
}

.alert h3 {
  margin: 0 0 8px;
  font-size: 17px;
  color: #92400e;
}

.alert p {
  margin: 0;
  font-size: 15px;
  color: #78350f;
}

/* Env table */
.env-table {
  width: 100%;
  border-collapse: collapse;
  background: var(--color-card);
  border-radius: 12px;
  overflow: hidden;
  border: 1px solid var(--color-border);
}

.env-table th, .env-table td {
  padding: 14px 20px;
  text-align: left;
  font-size: 15px;
  border-bottom: 1px solid var(--color-border);
}

.env-table tr:last-child th,
.env-table tr:last-child td {
  border-bottom: none;
}

.env-table th {
  background: #f1f5f9;
  width: 30%;
  color: var(--color-text-soft);
  font-weight: 600;
}

/* Links */
.links {
  background: var(--color-card);
  border-radius: 12px;
  padding: 20px 24px 20px 44px;
  border: 1px solid var(--color-border);
}

.links li {
  margin: 6px 0;
  font-size: 15px;
}

.links a {
  color: var(--color-primary-dark);
}

/* Footer */
footer {
  background: #0f172a;
  color: #cbd5e1;
  padding: 24px 0;
  text-align: center;
  font-size: 13px;
  margin-top: 56px;
}

footer p { margin: 0; }

/* Mobile */
@media (max-width: 640px) {
  .hero { padding: 40px 0 32px; }
  .hero h1 { font-size: 32px; }
  .download-btn { padding: 16px 24px; font-size: 16px; }
  main section { padding: 40px 0; }
  main h2 { font-size: 22px; }
  .steps li { padding: 18px; gap: 14px; }
  .step-num { width: 38px; height: 38px; font-size: 17px; }
  .env-table th { width: 38%; }
}