How to make specific button disappear - php

Question

I am newbie at website programming. This is for my school 'end of the year' project. I need to know how to make upvote/downvote system. I managed to make +1 and -1 buttons for each of my posts, but when I want them to disappear when clicked all of them disappear (instead of only the specific one). The +1 and -1 works for individual posts but my solution does not work. example: When I click button +1 on post id=2 all of +1 buttons disappear and so on. I would like to know the solution for my problem. Thanks in advance
while ($forum = $vysledek->fetch_assoc())
{
if (isset($_SESSION['upvote'])) {
$type = 'hidden';
}
else
{
$type = 'button';
}
if (isset($_SESSION['downvote'])) {
$type1 = 'hidden';
}
else
{
$type1 = 'button';
}
?>
<a href='votes.php?pris=<?php echo $forum['id_prispevek'] ?> & ad_id=1'>
<input type="<?php echo $type ?>" value="+1"></a>
<a href='votes.php?pris=<?php echo $forum['id_prispevek'] ?> & ad_id=0'>
<input type="<?php echo $type1 ?>" value="-1"></a>
}
and on votes.php
<?php
include "pripojeni1.php";
$var_value = $_GET['ad_id'];
$prispevek = $_GET['pris'];
if ($var_value == 1) {
$query = mysqli_query($link,"
UPDATE forum
SET votes = votes + 1
WHERE id_prispevek = '".$prispevek."'
");
header("location:vypisForum.php?var=$prispevek");
$_SESSION['upvote'] = 1;
unset($_SESSION['downvote']);
}
if ($var_value == 0) {
$query = mysqli_query($link,"
UPDATE forum
SET votes = votes - 1
WHERE id_prispevek = '".$prispevek."'
");
header("location:vypisForum.php?var=$prispevek");
$_SESSION['downvote'] = 1;
unset($_SESSION['upvote']);
}
?>