I know this is sort of late, but maybe it will help someone else…
Go to plugins/age-verify/includes/class-age-verify.php line 204
Change it to this:
#av-overlay {
background: #<?php echo esc_attr( av_get_overlay_color() ); ?>;
text-align:center;
}
Then, in the same file, go this line:
<div id="av-overlay">
and under it place the hard-coded logo image you would like to use:
<div id="av-overlay">
<img src="https://www.domain.com/wp-content/uploads/image_name.png" width="200" height="203" alt="ALT" />
<h1><?php esc_html_e( av_get_the_heading() ); ?></h1>
This will add your logo image at the top and center everything within the div.