diff --git a/custom_theme/404.html b/custom_theme/404.html
new file mode 100644
index 00000000..4ce71946
--- /dev/null
+++ b/custom_theme/404.html
@@ -0,0 +1,7 @@
+{% extends "main.html" %}
+
+{% block content %}
+    <h1>Page Not Found</h1>
+    <p>The page you have requested was not found.</p>
+    <p><a href="/">Go back to the documentation home</a>.</p>
+{% endblock %}
diff --git a/mkdocs.yml b/mkdocs.yml
index 6528b238..e3816bd8 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -76,6 +76,7 @@ theme:
   font:
     text: Roboto
     code: Roboto Mono
+  custom_dir: 'custom_theme'
 
 plugins:
   - mkdocstrings