How to lock an image block in a text block

You can use this code to Website > Website Tools > Custom CSS

div#block-55e87f66b5f57420ac52:after {
    content: "";
    background-image: url(https://images.squarespace-cdn.com/content/v1/5fef9103e1367528108f3716/2671be9c-b111-4f27-a8c1-1ade3985eac3/signature+%285%29.png?format=300w);
    background-size: contain;
    background-repeat: no-repeat;
    display: block;
    width: 250px;
    height: 70px;
}