/* Era 3: 2010年代風 — フラットデザイン、白基調、Sans-serif */
body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Helvetica Neue', Arial, sans-serif;
  background: #f5f5f5;
  color: #222;
  margin: 0;
  padding: 0;
  line-height: 1.6;
}
main {
  max-width: 720px;
  margin: 32px auto;
  padding: 32px;
  background: white;
  border-radius: 8px;
  box-shadow: 0 2px 12px rgba(0, 0, 0, 0.06);
}
h1 {
  color: #1976d2;
  font-size: 28px;
  font-weight: 600;
  margin: 0 0 24px;
  letter-spacing: -0.01em;
}
p { color: #333; margin: 0 0 16px; }
a { color: #1976d2; text-decoration: none; }
a:hover { text-decoration: underline; }
hr { border: 0; height: 1px; background: #e0e0e0; margin: 24px 0; }
button, input[type=submit] {
  background: #1976d2;
  color: white;
  border: none;
  padding: 10px 20px;
  border-radius: 4px;
  font-family: inherit;
  font-size: 14px;
  cursor: pointer;
}
button:hover, input[type=submit]:hover { background: #1565c0; }
input[type=text], input[type=password] {
  border: 1px solid #ddd;
  border-radius: 4px;
  padding: 8px 12px;
  font-size: 14px;
  font-family: inherit;
}
.stage-no {
  color: #999;
  font-size: 11px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}
code {
  background: #f0f0f0;
  padding: 2px 6px;
  border-radius: 3px;
  font-family: 'SF Mono', Consolas, 'Courier New', monospace;
  font-size: 0.92em;
  color: #d63384;
}
.card {
  background: #fafafa;
  border: 1px solid #e0e0e0;
  border-radius: 6px;
  padding: 20px;
  margin: 12px 0;
}