* {
    padding: 0;
    margin: 0;
}

body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #f4f4f9;
    font-family: Arial, sans-serif;
}

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

#display {
    box-sizing: border-box;
    width: 100%;
    height: 70px;
    font-size: 24px;
    text-align: right;
    margin-bottom: 10px;
    padding: 10px;
    border-radius: 5px;
    background: #eee;
}

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

button {
    height: 60px;
    border-radius: 5px;
    border: none;
    font-size: 18px;
    cursor: pointer;
    background-color: #555;
    color: white;
    transition: 0.2s;
}

button:hover {
    background-color: #777;
}

.operator {
    background-color: #ff9500;
}

.equal {
    background-color: #2ecc71;
    grid-row: span 2;
    height: 130px;
}

.zero {
    grid-column: span 2;
}