body {
  margin: 0;
  font-family: "Segoe UI", sans-serif;
  background-color: #f4f6fa;
  color: #222;
}

header {
  background-color: #ffffff;
  padding: 15px 40px;
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.logo {
  font-weight: bold;
  color: #1e3a8a;
  font-size: 22px;
}

nav ul {
  list-style: none;
  display: flex;
  gap: 20px;
  margin: 0;
  padding: 0;
}

nav ul li a {
  text-decoration: none;
  color: #1e3a8a;
  font-weight: 500;
  transition: 0.3s;
}

nav ul li a:hover,
nav ul li a.active {
  color: #1e88e5;
}

.layout {
  display: flex;
  padding: 30px;
}

.sidebar {
  width: 220px;
  background-color: white;
  border-radius: 12px;
  padding: 20px;
  box-shadow: 0 5px 10px rgba(0, 0, 0, 0.05);
  margin-right: 30px;
}

.sidebar h3 {
  color: #1e3a8a;
  margin-bottom: 15px;
}

.sidebar ul {
  list-style: none;
  padding: 0;
}

.sidebar li {
  margin-bottom: 12px;
}

.sidebar li a {
  text-decoration: none;
  color: #333;
  padding: 10px;
  display: block;
  border-radius: 6px;
  transition: background 0.3s;
}

.sidebar li a:hover,
.sidebar li.active a {
  background-color: #1e3a8a;
  color: white;
}

.challenge-content {
  flex: 1;
  background-color: white;
  padding: 30px;
  border-radius: 12px;
  box-shadow: 0 8px 20px rgba(0, 0, 0, 0.06);
}

.challenge-content h2 {
  color: #1e3a8a;
  margin-bottom: 20px;
}

textarea#codeInput {
  width: 100%;
  height: 200px;
  font-family: monospace;
  font-size: 14px;
  padding: 15px;
  border-radius: 8px;
  border: 1px solid #ccc;
  margin-top: 15px;
}

button#checkBtn {
  background-color: #1e88e5;
  color: white;
  border: none;
  padding: 10px 20px;
  font-weight: bold;
  margin-top: 15px;
  border-radius: 6px;
  cursor: pointer;
  transition: 0.3s;
}

button#checkBtn:hover {
  background-color: #1669c1;
}

.output-box {
  background-color: #f1f8e9;
  padding: 15px;
  border-radius: 10px;
  font-family: monospace;
  margin-top: 15px;
  white-space: pre-wrap;
  color: #2e7d32;
  border: 1px solid #c5e1a5;
}

#feedback {
  margin-top: 15px;
  font-weight: bold;
}

footer {
  text-align: center;
  padding: 20px;
  background-color: #1e3a8a;
  color: white;
  margin-top: 40px;
}