body {
  margin: 0;
  font-family: 'Fira Code', monospace;
  background-color: #0e0e0e;
  color: #e0e0e0;
  display: flex;
}
.sidebar {
  width: 240px;
  background-color: #161616;
  height: 100vh;
  padding: 20px;
  border-right: 2px solid #222;
}
.sidebar h2 {
  color: #66fcf1;
  font-size: 20px;
}
.sidebar ul {
  list-style: none;
  padding: 0;
}
.sidebar li {
  margin: 15px 0;
}
.sidebar a {
  color: #ccc;
  text-decoration: none;
  font-size: 16px;
}
.main {
  flex-grow: 1;
  padding: 30px;
}
header {
  font-size: 28px;
  margin-bottom: 20px;
  color: #66fcf1;
}
.container {
  background-color: #1f1f1f;
  padding: 25px;
  border-radius: 10px;
  max-width: 800px;
  margin: auto;
}
select, input, button {
  width: 100%;
  padding: 12px;
  font-size: 16px;
  border-radius: 6px;
  margin-top: 10px;
  border: none;
}
select, input {
  background-color: #2a2a2a;
  color: #fff;
}
button {
  background-color: #66fcf1;
  color: #000;
  font-weight: bold;
}
.challenge {
  margin-top: 20px;
  padding: 20px;
  background-color: #2a2a2a;
  border-left: 4px solid #66fcf1;
  border-radius: 8px;
}
pre {
  background-color: #111;
  padding: 10px;
  border-radius: 5px;
  margin-top: 15px;
  color: #00ff7f;
}