* {
  box-sizing: border-box;
  font-family: system-ui, sans-serif;
}

body {
  margin: 0;
  background: #f7f8fa;
  color: #222;
}

.container {
  max-width: 420px;
  margin: 60px auto;
  padding: 20px;
  background: #ffffff;
  border-radius: 12px;
  box-shadow: 0 10px 25px rgba(0,0,0,0.08);
  text-align: center;
}

h1 {
  margin-bottom: 5px;
}

.subtitle {
  color: #666;
  margin-bottom: 30px;
}

.calculator input {
  width: 100%;
  padding: 12px;
  margin-bottom: 10px;
  font-size: 16px;
}

.calculator span {
  display: block;
  margin: 8px 0;
  color: #555;
}

button {
  width: 100%;
  padding: 12px;
  font-size: 16px;
  background: #2563eb;
  color: white;
  border: none;
  border-radius: 8px;
  cursor: pointer;
}

button:hover {
  background: #1d4ed8;
}

.result {
  margin-top: 20px;
  font-size: 18px;
  font-weight: bold;
}

footer {
  text-align: center;
  margin-top: 40px;
  color: #888;
  font-size: 14px;
}