body {
  background: #2c2c2c;
  font-family: sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}

.calculator {
  background: #000;
  padding: 20px;
  border-radius: 30px;
  box-shadow: 0px 10px 25px rgba(0,0,0,0.5);
  text-align: center;
  width: 320px;
}

.calculator h2 {
  color: white;
  margin-bottom: 15px;
}

#display {
  width: 18rem;
  height: 80px;
  border: none;
  text-align: right;
  padding: 0 15px;
  font-size: 30px;
  border-radius: 10px;
  background: #333;
  color: white;
  margin-bottom: 30px;
  margin-top: 30px;
}

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

.btn {
  padding: 20px;
  font-size: 20px;
  border: none;
  border-radius: 50%;
  cursor: pointer;
  transition: 0.2s;
}

.btn.gray {
  background: #a5a5a5;
  color: black;
}

.btn.orange {
  background: #f89c0e;
  color: white;
}

.btn.dark {
  background: #333;
  color: white;
}

.btn:hover {
  opacity: 0.8;
}

.btn.wide {
  grid-column: span 2;
  border-radius: 35px;
}