php check doesn't reconnect to admin panel - php

Question

I'm trying to make admin panel, but in login page when username and password are submitted it just redirects me to the php where it is checking the data, it won't reconnect to the admin panel.. Here is the code:
This is where you input username and password (connection and session are included in head of the document):
<header>
<div class="body" style="padding-top: 150px;">
<div class="border rounded shadow login-center">
<form action="provjera.php" method="POST" style="padding-top: 32px;">
<div class="form-group text-center"><img class="img-fluid" style="width: 100px;" src="../assets/img/logo.png"></div>
<div class="form-group d-flex justify-content-center"><input class="form-control" type="text" name="ime" style="width: 200px;" placeholder="Korisničko ime"></div>
<div class="form-group d-flex justify-content-center"><input class="form-control" type="password" name="sifra" style="width: 200px;" placeholder="Šifra"></div>
<div class="form-group d-flex justify-content-center"><input class="btn btn-dark" style="width: 200px;" type="submit"></div>
</form>
</div>
</div>
and this is the "provjera.php" that is checking the data:
<?php
session_start();
$konekcija = mysqli_connect('localhost', 'root','' );
if($konekcija){
echo "conenction successful";
}else{
echo "no connection";
}
$baza=mysqli_select_db($konekcija,'hotel');
if(isset($_POST['submit'])){
$username = $_POST['ime'];
$password = $_POST['sifra'];
$sql = " select * from korisnik where ime='$username' and sifra='$password' ";
$query = mysqli_query($konekcija,$sql);
$row = mysqli_num_rows($query);
if($row == 1){
echo "login successful";
$_SESSION['ime'] = $username;
header('location:panel.php');
}else{
echo "login failed";
header('location:odjava.php');
}
}
?>