/** @format */

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
html {
  font-size: 62.5%;
}
body {
  font-family: Arial, sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
  background: black;
}

.calculator {
  background: #fff;
  border-radius: 10px;
  box-shadow: 0 5px 15px rgba(0, 0, 0, 0.2);
  width: 30rem;
  padding: 20px;
}

.display {
  margin-bottom: 20px;
}

.display input {
  width: 100%;
  height: 60px;
  font-size: 1.5rem;
  text-align: right;
  border: 1px solid #ddd;
  border-radius: 5px;
  padding: 10px;
  box-sizing: border-box;
  background: #f9f9f9;
}

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

.btn {
  font-size: 14px;
  padding: 15px 0;
  text-align: center;
  border: none;
  border-radius: 5px;
  cursor: pointer;
  background: #4caf50;
  color: white;
  transition: background 0.3s;
}

.btn.operator {
  background: #ff9800;
}

.btn.equal {
  grid-column: span 4;
  background: #2196f3;
}

.btn:hover {
  opacity: 0.9;
}

#clear {
  background: #f44336;
}