/* General body style */
body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: linear-gradient(135deg, #6a11cb, #2575fc);
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  margin: 0;
}

/* Calculator container */
.calculator {
  background-color: #1e1e1e;
  padding: 20px;
  border-radius: 20px;
  box-shadow: 0 10px 30px rgba(0,0,0,0.3);
  width: 280px;
}

/* Display */
.display {
  background-color: #333;
  color: #fff;
  font-size: 2em;
  text-align: right;
  padding: 15px;
  border-radius: 10px;
  margin-bottom: 15px;
  overflow-x: auto;
}

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

/* General button style */
.btn {
  padding: 20px;
  font-size: 1.2em;
  border: none;
  border-radius: 10px;
  background-color: #444;
  color: #fff;
  cursor: pointer;
  transition: all 0.2s ease;
  box-shadow: 0 5px #222;
}

/* Hover & active effect */
.btn:hover {
  background-color: #555;
}

.btn:active {
  transform: translateY(2px);
  box-shadow: 0 3px #222;
}

/* Special buttons */
.btn.operator {
  background-color: #f39c12;
  color: #fff;
}

.btn.operator:hover {
  background-color: #e67e22;
}

.btn.equal {
  background-color: #27ae60;
  grid-row: span 2;
}

.btn.equal:hover {
  background-color: #2ecc71;
}

.btn.clear {
  background-color: #e74c3c;
}

.btn.clear:hover {
  background-color: #c0392b;
}