You can use this code to Custom CSS box. Replace Pixabay with your logo image URL.

footer.sections:before {
    content: "";
    background-image: url(https://images.squarespace-cdn.com/content/v1/644f2654b9c076768430cf4b/2c193ec8-9ecc-446a-ad0a-b50aa57d8a51/Rectangle%2B27.jpg?format=1500w);
    background-size: contain;
    background-repeat: no-repeat;
    background-position: center center;
    width: 100px;
    height: 100px;
    top: -50px;
    position: absolute;
    z-index: 99999999;
    left: 50%;
    transform: translateX(-50%);
}
footer.sections {
    position: relative;
    z-index: 99999999999 !important;
}

Note:

Top = ½ Height

Result: