/* ============================================================
   common.css — 共通スタイル
   「いまさら聞けない！AIの初歩の初歩をゆるりと語ろうの会」
   bY community / YAMAGA BASE Inc.
   ============================================================ */

@import url('https://fonts.googleapis.com/css2?family=Noto+Sans+JP:wght@300;400;500;700;900&family=Inter:wght@300;400;600;700;900&display=swap');

/* --- CSS Variables --- */
:root {
  --bg: #0a0a1a;
  --card-bg: rgba(255,255,255,0.03);
  --border: rgba(255,255,255,0.08);
  --text: #f0f0ff;
  --text-dim: #8888aa;
  --green: #10b981;
  --green-bg: rgba(16,185,129,0.06);
  --green-border: rgba(16,185,129,0.25);
  --orange: #f59e0b;
  --orange-bg: rgba(245,158,11,0.06);
  --orange-border: rgba(245,158,11,0.25);
  --blue: #4f8fff;
  --blue-bg: rgba(79,143,255,0.06);
  --blue-border: rgba(79,143,255,0.25);
  --purple: #8b5cf6;
  --pink: #ec4899;
  --cyan: #06b6d4;
}

/* --- Reset & Base --- */
* { margin: 0; padding: 0; box-sizing: border-box; }

body {
  font-family: 'Noto Sans JP', 'Inter', sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
}

a { color: var(--blue); text-decoration: none; }
a:hover { text-decoration: underline; }

/* --- Shared heading gradient --- */
.gradient-heading {
  font-weight: 900;
  background: linear-gradient(135deg, var(--green), var(--orange), var(--blue));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

/* --- Back-to-hub link --- */
.back-to-hub {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  color: var(--blue);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 600;
  padding: 10px 20px;
  border-radius: 10px;
  border: 1px solid var(--blue-border);
  background: var(--blue-bg);
  transition: background 0.2s;
}
.back-to-hub:hover {
  background: rgba(79,143,255,0.12);
  text-decoration: none;
}

/* --- Back-to-top button --- */
.back-to-top {
  position: fixed;
  bottom: 28px;
  right: 28px;
  z-index: 100;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  border: 1px solid rgba(255,255,255,0.12);
  background: rgba(18,18,42,0.9);
  backdrop-filter: blur(10px);
  color: var(--text);
  font-size: 1.1rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.3s, background 0.2s, transform 0.2s;
}
.back-to-top.visible {
  opacity: 1;
  pointer-events: auto;
}
.back-to-top:hover {
  background: rgba(79,143,255,0.2);
  transform: translateY(-2px);
}

/* --- Footer --- */
.site-footer {
  text-align: center;
  margin-top: 50px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
  color: var(--text-dim);
  font-size: 0.8rem;
}

.site-footer .footer-nav {
  margin-bottom: 16px;
}

.site-footer .footer-logo {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  margin-top: 18px;
  margin-bottom: 8px;
}

.site-footer .footer-logo img {
  height: 96px;
  background: rgba(255,255,255,0.95);
  border-radius: 14px;
  padding: 14px 20px;
}

.site-footer .footer-logo .presents {
  font-size: 0.72rem;
  color: var(--text-dim);
  letter-spacing: 0.05em;
}

.site-footer .footer-credit {
  margin-top: 4px;
  font-size: 0.75rem;
  color: rgba(255,255,255,0.3);
}

.site-footer .footer-copyright {
  margin-top: 10px;
  font-size: 0.7rem;
  color: rgba(255,255,255,0.2);
}

/* --- Last updated badge --- */
.last-updated {
  display: inline-block;
  font-size: 0.72rem;
  padding: 3px 12px;
  border-radius: 16px;
  background: rgba(255,255,255,0.04);
  border: 1px solid var(--border);
  color: var(--text-dim);
  margin-top: 10px;
}

/* --- Header logo (hub page) --- */
.header-branding {
  margin-bottom: 18px;
}

.header-branding img {
  height: 120px;
  background: rgba(255,255,255,0.95);
  border-radius: 16px;
  padding: 16px 24px;
}

.header-branding .presents {
  display: block;
  font-size: 0.78rem;
  color: var(--text-dim);
  margin-top: 8px;
  letter-spacing: 0.05em;
}

/* --- Print --- */
@media print {
  body { background: white; color: #222; }
  .back-to-top { display: none; }
  .back-to-hub { display: none; }
  .site-footer { color: #888; border-color: #ddd; }
  .site-footer .footer-logo img { filter: grayscale(1); }
  .gradient-heading { -webkit-text-fill-color: #333; }
}

/* --- Responsive base --- */
@media (max-width: 600px) {
  .back-to-top { bottom: 16px; right: 16px; width: 40px; height: 40px; }
}