body {
display: flex;
justify-content: center;
align-items: center;
height: 100vh;
background-color: #f0f2f5;
font-family: Arial, sans-serif;
margin: 0;
}

.calculator {
background-color: #333;
padding: 20px;
border-radius: 10px;
box-shadow: 0px 4px 10px rgba(0, 0, 0, 0.3);
width: 320px;
}

#display {
width: 100%;
height: 60px;
background-color: #222;
color: #fff;
border: none;
font-size: 2rem;
text-align: right;
padding: 10px;
box-sizing: border-box;
border-radius: 5px;
margin-bottom: 20px;
}

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

.btn {
padding: 20px;
font-size: 1.2rem;
border: none;
border-radius: 5px;
cursor: pointer;
background-color: #e0e0e0;
transition: background 0.2s;
}

.btn:hover {
background-color: #d4d4d4;
}

.operator {
background-color: #ff9500;
color: white;
}

.operator:hover {
background-color: #e08500;
}

.clear {
background-color: #ff3b30;
color: white;
}

.clear:hover {
background-color: #d32f2f;
}

.equal {
background-color: #34c759;
color: white;
grid-row: span 2;
}

.equal:hover {
background-color: #28a745;
}

.zero {
grid-column: span 1;
}