add 404/403 pages

templates/404.html

@@ -0,0 +1,19 @@
+{% extends "base.html" %}
+{% block title %}404 · Page Not Found · myboker.org{% endblock %}
+{% block page_class %}page--error{% endblock %}
+{% block content %}
+
+<div class="error-pg">
+    <div class="error-pg__suit" aria-hidden="true">♠</div>
+    <div class="error-pg__body">
+        <span class="error-pg__code">404</span>
+        <h1 class="error-pg__title">Page not found.</h1>
+        <p class="error-pg__sub">That URL doesn't exist or the page has been moved. Double-check the address or head back to safety.</p>
+        <div class="error-pg__actions">
+            <a class="btn btn--primary btn--lg" href="{{ url_for('public.home') }}">Go home →</a>
+            <a class="btn btn--ghost btn--lg" href="javascript:history.back()">Go back</a>
+        </div>
+    </div>
+</div>
+
+{% endblock %}