* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  letter-spacing: 1px;
}

body {
  min-height: 100vh;
  max-width: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
}

.calculator {
  background: #f4f4f4;
  border-radius: 15px;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.3);
  padding: 20px;
  width: 320px;
  max-width: 90vw;
}

.display {
  margin-bottom: 20px;
}

#inputBox {
  width: 100%;
  height: 80px;
  border: none;
  border-radius: 10px;
  background: #fff;
  box-shadow: inset 0 2px 5px rgba(0, 0, 0, 0.1);
  font-size: 2rem;
  text-align: right;
  padding: 0 20px;
  color: #333;
  outline: none;
}

.row {
  display: flex;
  justify-content: space-between;
  margin-bottom: 10px;
}

button {
  width: 70px;
  height: 70px;
  border: none;
  border-radius: 10px;
  font-size: 1.5rem;
  font-weight: bold;
  cursor: pointer;
  transition: all 0.2s ease;
  background: #e0e0e0;
  color: #333;
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.1);
}

button:hover {
  background: #d0d0d0;
  transform: translateY(-2px);
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.2);
}

button:active {
  transform: translateY(0);
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.1);
}

.operator {
  background: #ff9500;
  color: #fff;
}

.operator:hover {
  background: #e88500;
}

#equal-button {
  background: #4caf50;
  color: #fff;
}

#equal-button:hover {
  background: #45a049;
}

#plusMinus {
  background: #2196f3;
  color: #fff;
}

#plusMinus:hover {
  background: #0b7dda;
}

@media (max-width: 400px) {
  .calculator {
    width: 280px;
    padding: 15px;
  }

  button {
    width: 60px;
    height: 60px;
    font-size: 1.2rem;
  }

  #inputBox {
    height: 60px;
    font-size: 1.5rem;
  }
}