body {
  background-color: #fff;
  color: #ffffff;
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
}

.calculator {
  background-color: #2d2d2d;
  border-radius: 15px;
  padding: 20px;
  width: 100%;
  max-width: 300px;
  box-shadow: 0 10px 25px rgba(0, 0, 0, 0.5);
}

.display {
  margin-bottom: 15px;
}

#result {
  background-color: #1a1a1a;
  color: #ffffff;
  font-size: 2em;
  text-align: right;
  padding: 15px;
  border: none;
  border-radius: 8px;
  margin-bottom: 10px;
  height: 60px;
}

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

.btn {
  padding: 15px;
  font-size: 1.2em;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.2s;
}

.btn-dark {
  background-color: #3d3d3d;
  color: white;
}

.btn-dark:hover {
  background-color: #4d4d4d;
}

.btn-warning {
  background-color: #ff9500;
  color: white;
}

.btn-warning:hover {
  background-color: #ffaa33;
}

.btn-primary {
  background-color: #007bff;
}

.btn-primary:hover {
  background-color: #3395ff;
}

.btn-secondary {
  background-color: #5c5c5c;
  color: white;
}

.btn-secondary:hover {
  background-color: #6d6d6d;
}

.zero {
  grid-column: span 2;
}

.equals {
  grid-column: span 1;
}