body {
  font-family: sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background-color: #f0f0f0;
}

.calculator {
  background: white;
  border-radius: 10px;
  box-shadow: 0 4px 20px rgba(0,0,0,0.2);
  padding: 20px;
  width: 350px;
}

.display {
  width: 100%;
  height: 50px;
  font-size: 24px;
  margin-bottom: 10px;
  text-align: right;
  padding: 10px;
  box-sizing: border-box;
  border: 1px solid #ccc;
  border-radius: 5px;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 10px;
}

button {
  padding: 20px;
  font-size: 20px;
  border: none;
  border-radius: 5px;
  background: #e0e0e0;
  cursor: pointer;
}

button:hover {
  background: #d0d0d0;
}

button.invisible {
  background: transparent;
  border: none;
  pointer-events: none;
}


@media (max-width: 480px) {
  .calculator {
    width: 90%;
    padding: 10px;
  }

  .display {
    font-size: 20px;
    height: 40px;
  }

  button {
    padding: 15px;
    font-size: 18px;
  }
}