body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Arial, sans-serif;
  margin: 0;
  padding: 0;
  background: linear-gradient(135deg, #f5f7fa, #c3cfe2);
  color: #333;
  text-align: center;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}
header {
  padding: 60px 20px 20px;
}
.logo {
  width: 80px;
  height: 80px;
  margin-bottom: 10px;
}
h1 {
  font-size: 2.4rem;
  margin: 0.5em 0;
}
.subtitle {
  font-size: 1.1rem;
  color: #555;
}
main {
  flex: 1;
  padding: 0 20px;
}
.btn {
  display: inline-block;
  background: #4a90e2;
  color: white;
  padding: 10px 20px;
  margin-top: 20px;
  border-radius: 8px;
  text-decoration: none;
  transition: background 0.2s;
}
.btn:hover {
  background: #357ab8;
}
footer {
  padding: 15px;
  font-size: 0.9rem;
  color: #666;
}
.back {
  display: inline-block;
  color: #4a90e2;
  text-decoration: none;
  margin-top: 20px;
}