body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    background-color: #f4f4f4;
    font-family: Arial, sans-serif;
}

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

.display {
    background-color: #222;
    color: #fff;
    text-align: right;
    padding: 20px;
    font-size: 2em;
    border-radius: 10px;
    margin-bottom: 20px;
    min-height: 40px;
    word-wrap: break-word;
}

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

.btn {
    width: 60px;
    height: 60px;
    border-radius: 50%;
    border: none;
    font-size: 1.2em;
    cursor: pointer;
    background-color: #555;
    color: white;
    transition: background-color 0.2s;
    display: flex;
    justify-content: center;
    align-items: center;
}

.btn:hover {
    background-color: #777;
}

.btn:active {
    background-color: #999;
}

.operator {
    background-color: #f39c12;
}

.operator:hover {
    background-color: #e67e22;
}

.clear {
    background-color: #e74c3c;
}

.clear:hover {
    background-color: #c0392b;
}

.equal {
    background-color: #2ecc71;
}

.equal:hover {
    background-color: #27ae60;
}