Add 404 template

templates/404.html

@@ -0,0 +1,8 @@
+{% extends "skel.html" %}
+{% block html_title %}Matrix.org - Not Found{% endblock html_title %}
+{% block content %}
+<div class="content">
+    <h1>Not Found</h1>
+    <p>This page doesn't exist.</p>
+</div>
+{% endblock content %}

templates/includes/header.html

@@ -4,6 +4,8 @@
 {% set path = section.path %}
 {% elif taxonomy %}
 {% set path = current_path %}
+{% else %}
+{% set path = "" %}
 {% endif %}
 <header class="site-header">
     <a href="/" class="brand{% if path == '/' %} current{% endif %}">