body {
  font-family: Arial;
  margin: 0;
  background: #f5f7fa;
}

header {
  background: #0a2540;
  color: white;
  text-align: center;
  padding: 40px;
}

.calculator, .lead {
  padding: 30px;
  text-align: center;
}

input {
  display: block;
  margin: 10px auto;
  padding: 12px;
  width: 250px;
}

button {
  padding: 12px 20px;
  background: #0070f3;
  color: white;
  border: none;
  cursor: pointer;
}

footer {
  text-align: center;
  padding: 20px;
}