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

.calculator {
    border: 2px solid black;  
    padding: 20px;
    border-radius: 5px;
    width: 220px;  
}

#userInput {
    width: 100%;
    height: 40px;
    font-size: 24px;
    text-align: right;
    margin-bottom: 10px;
}

.btn {
    width: 45px;
    height: 45px;
    margin: 2px;
    font-size: 20px;
}