* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
    "Helvetica Neue", Arial, sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background-color: #000;
}

.calculator {
  width: 100%;
  max-width: 400px;
  margin: 20px;
}

.calculator-display {
  background-color: #333;
  color: white;
  font-size: 2.5rem;
  text-align: right;
  padding: 20px;
  border-radius: 10px 10px 0 0;
  overflow: hidden;
}

.calculator-buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1px;
}

.button {
  font-size: 1.5rem;
  padding: 20px;
  background-color: #505050;
  color: white;
  border: none;
  outline: none;
  cursor: pointer;
}

.button.gray {
  background-color: #a5a5a5;
  color: black;
}

.button.orange {
  background-color: #ff9500;
  color: white;
}

.button.double {
  grid-column: span 2;
}

.button:active {
  opacity: 0.7;
}

@media (max-width: 768px) {
  .calculator-display {
    font-size: 2rem;
    padding: 15px;
  }

  .button {
    font-size: 1.2rem;
    padding: 15px;
  }
}

@media (max-width: 480px) {
  .calculator-display {
    font-size: 1.5rem;
    padding: 10px;
  }

  .button {
    font-size: 1rem;
    padding: 10px;
  }
}