* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  background-color: #121212;
  color: white;
  font-family: 'Segoe UI', sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}

.calculator {
  background-color: #1e1e1e;
  padding: 20px;
  border-radius: 15px;
  box-shadow: 0px 0px 20px #00000080;
  width: 320px;
}

#display {
  width: 100%;
  height: 60px;
  background-color: #2a2a2a;
  color: #fff;
  border: none;
  font-size: 24px;
  padding: 10px;
  border-radius: 10px;
  text-align: right;
  margin-bottom: 20px;
}

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

button {
  padding: 20px;
  font-size: 18px;
  border: none;
  border-radius: 10px;
  background-color: #333;
  color: white;
  cursor: pointer;
  transition: 0.2s;
}

button:hover {
  background-color: #555;
}

.equal {
  grid-column: span 2;
  background-color: #ff9500;
}

.equal:hover {
  background-color: #ffa733;
}