body {
  margin: 0;
  background-color: #000;
  font-family: -apple-system, BlinkMacSystemFont, sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}

.calculator {
  width: 320px;
  background-color: #000;
  border-radius: 30px;
  padding: 20px;
  box-shadow: 0 0 20px #333;
}

.display {
  background-color: #000;
  color: #fff;
  font-size: 3rem;
  text-align: right;
  padding: 20px 10px;
  border-radius: 10px;
  min-height: 60px;
  box-sizing: border-box;
  overflow: hidden;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 15px;
  margin-top: 20px;
}

.btn {
  padding: 20px;
  font-size: 1.5rem;
  border: none;
  border-radius: 50%;
  cursor: pointer;
  transition: background 0.2s;
}

.btn.function {
  background-color: #a5a5a5;
  color: black;
}

.btn.operator {
  background-color: #ff9f0a;
  color: white;
}

.btn.number {
  background-color: #333;
  color: white;
}

.btn.equal {
  background-color: #ff9f0a;
  color: white;
}

.btn.zero {
  grid-column: span 2;
  border-radius: 50px;
  text-align: left;
  padding-left: 35px;
}