php Login fails with the right credentials

Question

I have a project that requires creating a system for a given scenario using php and mySQL. Another requirement is that it has to have logins for different users.

In my implementation it fails to authenticate even with the right credentials. I am using mysqli for this implementation. There are no syntactical errors and the field names and entered credentials are all correct.

The code in question (login.php):

<?php
    session_start(); // Starting Session
    $error=''; // Variable To Store Error Message
    if (isset($_POST['submit'])) {
        if (empty($_POST['username']) || empty($_POST['password'])) {
            $error = "Please enter a username and password";
        } else {
        // Define $username and $password
        $username=$_POST['username'];
        $password=$_POST['password'];
        // Calls the 'connect.php' to connect to the database and select the database
        require 'db/connect.php'; 
        // To protect MySQL injection for Security purpose
        $username = stripslashes($username);
        $password = stripslashes($password);
        $username = mysql_real_escape_string($username);
        $password = mysql_real_escape_string($password);

        // SQL query to fetch information of registerd users and finds user match.
        $result = $db->query("SELECT * FROM `users` WHERE 'usr_pwd'='$password' AND 'usr_name'='$username'");
        if ($result->num_rows == 1) {
            $_SESSION['login_user']=$username; // Initializing Session
            header("location: test.php"); // Redirecting To Other Page
        } else {
            $error = "Username or Password is invalid";
        }
        mysqli_close($db); // Closing Connection
        }
    }
?>

I've also linked the github repo to my code as is: https://github.com/gussippi/furniture-store