section {
  font-family: Arial, sans-serif;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  height: 100vh;
  background-color: #f4f4f4;
}
.display {
  font-size: 24px;
  font-weight: bold;
  padding: 10px;
  background-color: white;
  border-radius: 5px;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
  margin-bottom: 20px;
}
.userInput {
  padding: 10px;
  font-size: 16px;
  width: 300px;
  border: 2px solid #ccc;
  border-radius: 5px;
  outline: none;
}
.userInput:focus {
  border-color: #007BFF;
}
.error {
  margin-top: 10px;
  font-size: 18px;
  color: red;
}
.topnav {
  background-color: #333;
  overflow: hidden;
}
.topnav a {
  float: left;
  color: #f2f2f2;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
  font-size: 17px;
}
.topnav a:hover {
  background-color: #ddd;
  color: black;
}
.topnav a.active {
  background-color: #04AA6D;
  color: white;
}