/* 共通スタイル */
body {
  font-family: -apple-system, BlinkMacSystemFont, sans-serif;
  max-width: 820px;
  margin: 0 auto;
  padding: 1rem;
  line-height: 1.7;
  background: #fafafa;
  color: #333;
}

header, footer {
  text-align: center;
  margin: 1.5rem 0;
}

.site-nav a {
  margin: 0 8px;
  color: #4f46e5;
  text-decoration: none;
  font-weight: 600;
}

.site-nav a:hover {
  text-decoration: underline;
}

footer {
  font-size: 0.9em;
  color: #666;
}

header {
  position: relative;
}

.menu-toggle {
  display: none;
  position: absolute;
  top: 10px;
  right: 10px;
  background: none;
  border: none;
  font-size: 1.5em;
}

.mobile-sidebar,
.sidebar-overlay {
  display: none;
}

@media (max-width: 768px) {
  .site-nav { display: none; }
  .menu-toggle { display: block; }
  .mobile-sidebar,
  .sidebar-overlay { display: block; }
}

.mobile-sidebar {
  position: fixed;
  top: 0;
  right: -240px;
  width: 240px;
  height: 100%;
  background: #fff;
  box-shadow: -2px 0 5px rgba(0,0,0,0.3);
  padding: 20px;
  transition: right 0.3s;
  z-index: 1000;
  overflow-y: auto;
}

.mobile-sidebar nav a {
  display: block;
  margin-bottom: 10px;
  color: #333;
  text-decoration: none;
}

.mobile-sidebar.active { right: 0; }

.sidebar-overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: rgba(0,0,0,0.4);
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.3s;
  z-index: 999;
}

.sidebar-overlay.active {
  opacity: 1;
  visibility: visible;
}

.close-btn {
  background: none;
  border: none;
  font-size: 1.2em;
  align-self: flex-end;
  margin-bottom: 10px;
}