flask-bootstrap/templates/login.html

{% extends "base.html" %}

{% block title %}Login{% endblock %}

{% block main %}

<div id="login">
    <form method="POST">
        Username: <input type="text" name="username"/><br/>
        Password: <input type="password" name="password"/><br/>
        <input type="submit" class="btn" value="Log in"/>
    </form>
</div>

{% endblock %}