Remove shadow page

In your CSS file find this code

.wrapper {
    background-color: #FFFFFF;
    box-shadow: 0 0 5px rgba(0, 0, 0, 0.2);
}

and replace it with the code

.wrapper {
    background-color: #FFFFFF;
    box-shadow: 0 0 0px rgba(0, 0, 0, 0.2);
}

No! Do not edit the theme itself. First create a child theme for your changes. Or install a custom CSS plugin.