homepage pop-up window

Hello!

I would appriciate some help with the popups!
I’d like to make a fullscreen popup for my homepage, what is coming up in the 0.second.
i have got a blog and a webshop too, and i want to give the choice to the visitor to decide where to go next.
I tought that it would be a good idea, to use a popup window, with two pictures. One of them are leads to the webshop (sub-domain), and the other one closes the pop-up.
I have found a plugin.
https://www.ads-software.com/plugins/full-screen-popup/
The problem is, that i dont know what to do to close the popup with a picture. What script do i need, and where should i paste.

The original script for closing from the page source is:
<img id="closediv" onclick="javascript:fsp_hide_lightbox()" src="https://familiafitness.hu/wp-content/plugins/full-screen-popup/images/dbclose.png">
– in firefox

And i only found one file through the ftp, that mentioned this image (dbclose.png). the code looks like this

function xyz_fsp_display()
{
	$imgpath=plugins_url()."/full-screen-popup/images/";
	$closeimage=$imgpath."close.png";
	$dbcloseimage=$imgpath."dbclose.png";

	$html=get_option('xyz_fsp_html');

	$delay=get_option('xyz_fsp_delay');
	$page_count=get_option('xyz_fsp_page_count');
	if($page_count==0) $page_count=1;
	$mode=get_option('xyz_fsp_mode');
	$repeat_interval=get_option('xyz_fsp_repeat_interval');
	$repeat_interval_timing=get_option('xyz_fsp_repeat_interval_timing');
	if($repeat_interval_timing==1)
	{
		$repeat_interval=$repeat_interval*60;
	}
$z_index=get_option('xyz_fsp_z_index');
$corner_radius=get_option('xyz_fsp_corner_radius');

$border_color=get_option('xyz_fsp_border_color');
$bg_color=get_option('xyz_fsp_bg_color');

$border_width=get_option('xyz_fsp_border_width');

$iframe_option=get_option('xyz_fsp_iframe');

global $wpdb;

ob_flush();
ob_start();
	?>
	<style type="text/css">

.fsp_content {
display: none;
position: fixed;
_position: fixed;

top:0px;
left:0px;
width: 100%;
height: 100%;
padding: 0;
margin:0;
border: <?php echo $border_width; ?>px solid <?php echo $border_color;?>;
background-color: <?php echo $bg_color;?>;
z-index:<?php echo $z_index+1;?>;
overflow: hidden;
border-radius:<?php echo $corner_radius;?>px

}
.fsp_iframe{

width:100%;
height:100%;
border:0;

}

#closediv{
position:absolute;
cursor:pointer;
top: 0px;
right: 0px;
}
</style>

<div id="fsp_light" class="fsp_content"><?php if(!isset($_COOKIE['_xyz_fsp_until'])) {?>
<img id="closediv"   src="<?php  echo $dbcloseimage;?>" onclick = "javascript:fsp_hide_lightbox()"><?php ?>
<!-- <div width="100%" height="20px" style="text-align:right;padding:0px;margin:0px;"><a href = "javascript:void(0)" onclick = "javascript:fsp_hide_lightbox()">CLOSE</a></div> -->
<?php if($iframe_option==1) { ?><iframe  src="<?php echo  get_bloginfo('wpurl') ;?>/index.php?xyz_fsp=iframe" class="fsp_iframe" scrolling="no"></iframe><?php }else{
echo do_shortcode($html);}
}?>
</div>

I tried to change the close button with my image, it worked, but i cant place it where i wanted to.
So is there any solution for add plus “close” script for a picture?
Thanks for any help!!!