How to add overlay on scrollable div

Question

This is what I am getting Screen shot of table with overly in light white color

I wanted the overlay div to acquire all the table content

Answer 1

You can make put a div with below CSS styles.

div.overlay {
    position: fixed;
    top: 0;
    height: 70vw;
    width: 100%;
    z-index: 100
}

Answer 2

It was not possible what I wanted it to be

end up doing this