Use .twig instead of .html.twig

source/_partials/availability.twig

@@ -0,0 +1,27 @@
+<div class="availability">
+    <h2>Availability</h2>
+
+    <div class="content">
+        {% set now = "now"|date('U') %}
+
+        {% for type, data in site.availability.status %}
+            {% set text = site.availability.text[type][data.available] %}
+
+            {% if data.start %}
+                {% if data.start|date('U') > now %}
+                    {% set text = text ~ ' starting ' ~ data.start|date('F Y') %}
+
+                    {% if data.end %}
+                        {% set text = text ~ ',' %}
+                    {% endif %}
+                {% endif %}
+            {% endif %}
+
+            {% if data.end %}
+                {% set text = text ~ ' until ' ~ data.end|date('F Y') %}
+            {% endif %}
+
+            <p class="availability__{{ data.available }}">{{ text }}.</p>
+        {% endfor %}
+    </div>
+</div>