putting button inside code - php

Question

My working code outputs all the images in my wordpress post and puts the last image as the background of #last-img which is the last image shown.
I'm trying to place a button inside my code which appears inside the #last-img. I can't put it outside the code since when I tried when I use absolute positioning it uses all the images as a reference point
my code
<?php
preg_match_all('/(<img [^>]*>)/', get_the_content(), $images);
preg_match_all('/src="([^"]*)"/i', get_the_content(), $images1);
$count = count($images[1]);
$count1 = count($images1[1]);
foreach($images[1] as $k=> $img){
if($k == $count-1){
$format = '<div id="last-img" style="background:url(%s)"> ... </div>'; // Or $format = "<div id='last-img' style='background:url(%s)'> ... </div>";
$image = $images1[1][$count1-1];
echo sprintf($format,$image);
}else{
echo $img;
}
}
?>
link code
<div id="top-btn">
<div id="top-rotate"></div>
</div>
css
#top-btn {
display: block;
position: absolute;
z-index: 200;
right: 0; left: 0; bottom: 0;
margin: 0 auto;
height: 60px; width: 60px;
}