body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: #475f95;
  font-family: Arial;
}

.calculator {
  background: #ffffff;
  padding: 20px;
  border-radius: 20px;
  width: 280px;
  box-shadow: 0 10px 30px rgba(0,0,0,0.2);
  transition: transform 0.3s ease;
}

.calculator:hover {
  transform: scale(1.03);
}

#display {
  width: 100%;
  height: 60px;
  margin-bottom: 15px;
  font-size: 24px;
  text-align: right;
  padding: 10px;
  border: none;
  border-radius: 12px;
  background: #0f172a;
  color: #ffffff;
  box-shadow: inset 0 0 8px rgba(0,0,0,0.2);
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
}

button {
  padding: 18px;
  font-size: 18px;
  border: none;
  border-radius: 12px;
  cursor: pointer;
  background: #e5e7eb;
  color: #0f172a;
  transition: all 0.25s ease;
}

button:hover {
  background: #cbd5f5;
  transform: translateY(-3px);
  box-shadow: 0 5px 15px rgba(0,0,0,0.2);
}

button:active {
  transform: scale(0.95);
}

button:nth-child(4n) {
  background: #1e3a8a;
  color: white;
}

button:nth-child(4n):hover {
  background: #1e40af;
}

button:last-child {
  background: #2563eb;
  color: white;
}

button:last-child:hover {
  background: #3b82f6;
}

.zero {
  grid-column: span 2;
}