body {
  background-color: #0d0d0d;
  color: white;
  font-family: Arial, sans-serif;
  margin: 0;
  padding: 0;
}
header {
  background: #1a1a1a;
  padding: 10px;
  text-align: center;
}
nav a {
  margin: 0 10px;
  color: #ffcc00;
  text-decoration: none;
}
.card {
  background-color: #1a1a1a;
  border-left: 5px solid #ffcc00;
  margin: 20px;
  padding: 20px;
  border-radius: 8px;
}
.card.red { border-left-color: #ff4444; }
.card.yellow { border-left-color: #ffcc00; }
.card.green { border-left-color: #44ff44; }