dashboard register and login page

<html>
<head>
<title>Register</title></head>
<body>
<p><a href="register.php">Register</a> | <a href="loginn.php">Login</a></p>
<h3> Registration Form </h3>
<form action="" method="post">
username<input type="text" name="username"/></br>
email id:<input type="email" name="email" /></br>
password<input type="pass" name="password"/></br>
<input type="submit" name="send" value="send"></br>
</form>
<?php
include('db.php');
if(isset($_POST['send'])){
$username=$_POST['username'];
$email=$_POST['email'];
$password=$_POST['password'];
$sql="INSERT INTO login (username,email,password) VALUES ('$username','$email','$password')";
$result=mysqli_query($conn,$sql);
if ($result){
    echo "account successfully created";
}else {
    echo "Failure";
}
}
?>
</body>
</html>

LOGINN.PHP..................................

<?php
session_start();
include('db.php');

if(isset($_SESSION['username']))
{
  //$_SESSION['username'];
header("Location:home.php");
}
?>
<html>
<head>
<title>Register</title></head>
<body>
<p><a href="loginn.php">Login</a></p>
<h3>login</h3>
<form action=""  method="post">
username<input type="text" name="username"/></br>
password<input type="password" name="password"/></br>
<input type="submit" name="send" value="send"></br>
</form>
<?php
if(isset($_POST['send'])){
$username=$_POST['username'];
$password=$_POST['password'];

$query="SELECT * FROM login WHERE username= '$username' AND password= '$password'";
$res=mysqli_query($conn,$query);
$numrows=mysqli_num_rows($res);
//echo $numrows;
if($numrows)
{
$_SESSION['username']=$username;
//$_SESSION['pass']=$password;
//echo "valid username and password";
}
}
?>
</body>
</html>

HOME.PHP>>>>>>>>>>>>>.....

<?php
session_start();
if (!(isset($_SESSION['username']) )) {

header ("Location:loginn.php");

}
echo "welcome" .$_SESSION['username'];
?>
<a href= "logout.php"> Logout</a>
DB.PHP......................................................................
<html>
<head>
<title>Connection</title>
</head>
<body>
<?php
   $dbhost = 'localhost';
   $dbuser = 'root';
   $dbpass = '';
   $conn = mysqli_connect($dbhost, $dbuser, $dbpass);
   if(!$conn)
   {
     die('Could not connect: ' . mysqli_error());
   }
   //echo 'Connected successfully';
   //mysqli_select_db('information');
   mysqli_select_db($conn, "information");
  ?>
</body>
</html>

LOGOUT.PHP...................................

<?php
session_start();
if(isset($_SESSION['username']))
{
unset($_SESSION['username']);
header("Location:register.php");
exit();
}

?>

RETURN.PHP..............................................

<?php
    include('db.php');
        header("Location:register.php");
?>