body {
  font-family: "Segoe UI", sans-serif;
  background-color: #f4f4f4;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
}

.container {
  text-align: center;
  background: white;
  padding: 2rem;
  border-radius: 12px;
  box-shadow: 0 6px 20px rgba(0, 0, 0, 0.1);
  width: 300px;
}

h1 {
  margin-bottom: 1.5rem;
  color: #607d8b;
}

.display {
  font-size: 2.5rem;
  margin-bottom: 1.5rem;
  font-weight: bold;
  color: #333;
  background: #eee;
  padding: 1rem;
  border-radius: 8px;
  letter-spacing: 2px;
}

.buttons {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
}
.buttons button {
  flex: 1;
  padding: 0.6rem;
  border: none;
  border-radius: 6px;
  font-size: 1rem;
  cursor: pointer;
  transition: 0.3s ease;
}
.buttons button:nth-child(1) {
  background-color: #4caf50;
  color: white;
}
.buttons button:nth-child(2) {
  background-color: #f44336;
  color: white;
}
.buttons button:nth-child(3) {
  background-color: #607d8b;
  color: white;
}
.buttons button:hover {
  opacity: 0.85;
}
.buttons button:disabled {
  background-color: #d2e9d2;
}