Adding Bootstrap alerts as Flask flash messages

layout.html

{% with messages = get_flashed_messages() %} 
    {% if messages %}
    <ul class="flashes list-group">
        {% for message in messages %}
        <li class="list-group-item">
            <div class="alert alert-success">{{message}}</div>
        </li>
        {% endfor %}
    </ul>
    {% endif %} 
{% endwith %}

style.css

.list-group {
    margin: 10px 0;
}

.list-group-item {
    margin: 0;
    padding: 0;
}

.alert {
    margin: 0;
}