Reply To: Customizating the individual blog post view

This Additional CSS will change the background of the author and previous/next sections:

.single .entry-footer,
.single .post-navigation {
    background: #ffffff;
}

And use this to change the comments/reply section (I’ve also added some padding and rounded corners):

#comments {
    background: #ffffff;
    padding: 2em;
    border-radius: 2rem;
}

In the code above, the background color is #ffffff. Change this to the color you want.