.body, html {
    height: 100%;
    margin: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    background-image:url(./images/mathematics-background-DMY1XT.jpg);
}
.calculator-box {
    width: 85%; 
    margin: 0 auto;
    padding: 20px;
    border: 2px solid #c2bcbc;
    background-color: whitesmoke;
    border-radius: 10px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
}