Login not working

<?php
session_start();
?>
<html>
<head>

    <title>Login</title>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link rel="stylesheet" type="text/css" href="style.css">
</head>
<body>
<h1><img src="TBS.png" alt="Logo"/>
    <br>
    Login Page
</h1>
<ul id="menubar">
    <li><a href="homePage.php">Home</a></li>
    <li><a href="aboutus.html">About Us</a></li>
    <li><a href="contactus.html">Contact Us</a></li>
    <li><a href="loginPage.php">Login</a></li>
</ul>
<div>
    <br>
    <br>
    <br>
    <br>
    <ul id="textarea">
        Username:<br><input type="text" name="username"><br>
        Password:<br><input type="password" name="password"><br>
    </ul>


    <ul id="buttons">
        <input name="Login" type="submit" value="Login">
        <button><a href="homePage.php">Cancel</a></button>
    </ul>

    <?php

    if ($_POST['Login']) {
    include_once("database.php");
    $username = strip_tags($_POST['username']);
    $password = strip_tags($_POST['password']);

    $username = stripcslashes($username);
    $password = stripcslashes($password);

    $username = mysqli_real_escape_string($username);
    $password = mysqli_real_escape_string($password);

    $sql = "SELECT * FROM user WHERE username='$username'";
    $query = mysqli_query($db, $sql);
    $row = mysqli_fetch_array($query);
    $id = $row['id'];
    $db_password = $row['password'];

    if ($password == $db_password) {
        $_SESSION['username'] = $username;
        $_SESSION['id'] = $id;
        header("Location: homePage.php");
    } else {
        echo "you entered the wrong password";
    }
    }
    ?>
</div>
</body>
</html>