Add some base markdown styles

This is lighter-weight and arguably easier to configure that Tailwind's
typography plugin though I could switch to it at a later date if needed.

source/_partials/talk/events.html.twig

@@ -1,15 +1,17 @@
 {% if events is not empty %}
-    <h2>Events</h2>
+    <div class="markdown">
+        <h2>Events</h2>
 
-    <ul>
-        {% for event in events %}
-            {% include 'talk/events/event.html.twig' with {
-                date: event.date,
-                is_online: event.is_online ?? false,
-                location: event.location,
-                name: event.name,
-                url: event.url,
-            } only %}
-        {% endfor %}
-    </ul>
+        <ul>
+            {% for event in events %}
+                {% include 'talk/events/event.html.twig' with {
+                    date: event.date,
+                    is_online: event.is_online ?? false,
+                    location: event.location,
+                    name: event.name,
+                    url: event.url,
+                } only %}
+            {% endfor %}
+        </ul>
+    </div>
 {% endif %}