login.html

<!DOCTYPE html>
{% load static %}
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">

    <!-- Bootstrap CSS -->
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css"
          integrity="sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO" crossorigin="anonymous">

    <title>Startech</title>
</head>
<body>
<nav class="navbar justify-content-center navbar-dark bg-dark">
    <li class="nav-item">
        <a class="navbar-brand" href="home">Home</a>
    </li>
    <li class="nav-item">
        <a class="navbar-brand" href="">Laptop</a>
    </li>
    <li class="nav-item">
        <a class="navbar-brand" href="">Headphone</a>
    </li>
    <li class="nav-item">
        <a class="navbar-brand" href="">Mouse</a>
    </li>
    <li class="nav-item">
        <a class="navbar-brand" href="">Chair</a>
    </li>
    <li class="nav-item">
        <a class="navbar-brand" href="">Component</a>
    </li>
    {% if flag == 0 %}
        <ul class="nav justify-content-end">
            <li class="nav-item">
                <a class="navbar-brand" href="login">Log In</a>
            </li>

        </ul>

    {% elif flag == 1 %}
        <a class="navbar-brand" href="sales_entry">Sales</a>
        <ul class="nav justify-content-end">
            <li class="nav-item">
                <a class="navbar-brand" href="logout">Log Out</a>
            </li>
        </ul>
    {% elif flag == 2 %}
        <a class="navbar-brand" href="servicing">Servicing</a>
        <ul class="nav justify-content-end">
            <li class="nav-item">
                <a class="navbar-brand" href="logout">Log Out</a>
            </li>
        </ul>
    {% endif %}

</nav>
{% if messages %}
    <ul class="messages">
        {% for message in messages %}
            <li{% if message.tags %} class="{{ message.tags }}"{% endif %}>{{ message }}</li>
        {% endfor %}
    </ul>
{% endif %}

<div class="container">
    <div class="jumbotron">
        <h1 class="text-center">Log In</h1>
        <form method="POST" action="">
            {% csrf_token %}

            <br>
            <input type="text" class="form-control" placeholder="Username" name="username">
            <br>
            <input type="password" class="form-control" placeholder="Password" name="password">
            <br>
            <div class="text-center">
                <button type="submit" class="btn btn-primary">Submit</button>
            </div>

        </form>
    </div>
</div>

<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js"
        integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo"
        crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js"
        integrity="sha384-ZMP7rVo3mIykV+2+9J3UJ46jBk0WLaUAdn689aCwoqbBJiSnjAK/l8WvCWPIPm49"
        crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.min.js"
        integrity="sha384-ChfqqxuZUCnJSK3+MXmPNIyE6ZbWh2IMqE241rYiqJxyMiZ6OW/JmZQ5stwEULTy"
        crossorigin="anonymous"></script>
<script>
    if (window.history.replaceState) {
        window.history.replaceState(null, null, window.location.href);
    }
</script>
</body>
</html>