body {
  margin: 0;
  font-family: "Segoe UI", sans-serif;
  background-color: #f4f6fa;
}
header {
  background-color: #ffffff;
  display: flex;
  justify-content: space-between;
  padding: 15px 40px;
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}
.logo {
  font-weight: bold;
  font-size: 22px;
  color: #1e3a8a;
}
nav ul {
  display: flex;
  gap: 20px;
  list-style: none;
  padding: 0;
  margin: 0;
}
nav a {
  text-decoration: none;
  color: #1e3a8a;
  font-weight: 500;
  transition: 0.3s;
}
nav a:hover,
nav a.active {
  color: #1e88e5;
}
.layout {
  display: flex;
  padding: 30px 40px;
  gap: 30px;
}
.sidebar {
  background-color: white;
  width: 220px;
  padding: 20px;
  border-radius: 12px;
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.05);
}
.sidebar h3 {
  color: #1e3a8a;
}
.sidebar ul {
  list-style: none;
  padding: 0;
}
.sidebar li {
  margin-bottom: 10px;
}
.sidebar a {
  text-decoration: none;
  color: #1e3a8a;
  display: block;
  padding: 10px;
  border-radius: 6px;
  transition: 0.2s;
}
.sidebar a:hover,
.sidebar li.active a {
  background-color: #1e3a8a;
  color: white;
}
.challenge-content {
  flex: 1;
  background-color: white;
  padding: 25px;
  border-radius: 12px;
  box-shadow: 0 6px 20px rgba(0, 0, 0, 0.05);
}
.challenge-content h2 {
  color: #1e3a8a;
}
textarea {
  width: 100%;
  height: 260px;
  margin-top: 15px;
  padding: 12px;
  font-family: monospace;
  border-radius: 8px;
  border: 1px solid #ccc;
  font-size: 14px;
  resize: vertical;
}
button {
  background-color: #1e88e5;
  color: white;
  font-weight: bold;
  padding: 10px 18px;
  margin-top: 10px;
  border: none;
  border-radius: 6px;
  cursor: pointer;
}
button:hover {
  background-color: #1669c1;
}
.output-box {
  margin-top: 20px;
  background-color: #eaf4ea;
  color: #2e7d32;
  padding: 12px;
  border-radius: 8px;
  font-family: monospace;
  border: 1px solid #c8e6c9;
}
#feedback {
  margin-top: 15px;
  font-weight: bold;
}
footer {
  background-color: #1e3a8a;
  color: white;
  text-align: center;
  padding: 15px;
  margin-top: 40px;
}