app/templates/404.html

{% extends "base.html" %}

{% block content %}
    <div style="margin-top: 2em;" class="ui one column centered grid">
        <img alt="Error 404 Image" class="ui medium circular image" src="{{ url_for('static',filename='img/404.png') }}">
    </div>
    <div style="margin: 1.5em;" class="ui one column centered grid">
        <h2 class="ui header">This page is not on the map.</h2>
    </div>
{% endblock %}