* {
  padding: 0;
  margin: 0;
  box-sizing: border-box;
  font-family: "Poppins", sans-serif;
}

body {
  height: 100vh;
  background: linear-gradient(135deg, #667eea, #764ba2);
  display: flex;
  justify-content: center;
  align-items: center;
}

.calculator {
  width: 100%;
  max-width: 350px;
  background-color: #ffffff;
  padding: 20px;
  border-radius: 12px;
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.1);
}

.display {
  width: 100%;
  margin-bottom: 20px;
}

.display input {
  width: 100%;
  padding: 24px 16px;
  text-align: right;
  border: none;
  background-color: #f1f3f4;
  color: #333;
  font-size: 24px;
  border-radius: 8px;
  box-shadow: inset 0 2px 4px rgba(0, 0, 0, 0.1);
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

.buttons input[type="button"] {
  font-size: 18px;
  padding: 15px;
  border: none;
  background-color: #e0e0e0;
  color: #333;
  cursor: pointer;
  border-radius: 8px;
  transition: background-color 0.3s ease, transform 0.3s ease;
}

.buttons input[type="button"]:hover {
  background-color: #d4d4d4;
  transform: translateY(-2px);
}

input[type="button"]#equal {
  background-color: #e0e0e0;
  color: #333;
  grid-column: span 1;
}

input[type="button"]#equal:hover {
  background-color: #d4d4d4;
}

input[type="button"]#plus {
  background-color: #4caf50;
  color: #ffffff;
  grid-row: span 2;
}

input[type="button"]#plus:hover {
  background-color: #45a049;
}

@media (max-width: 400px) {
  .calculator {
    padding: 15px;
  }

  .buttons input[type="button"] {
    font-size: 16px;
    padding: 12px;
  }

  .display input {
    font-size: 20px;
  }
}