Centre one 42rem reading column on content, post, event and FAQ pages

Elternbeirat.Web/Features/Posts/PostList.razor.css

@@ -10,3 +10,20 @@
         grid-column: 1 / -1;
     }
 }
+
+/* Same centred 42rem reading column as a content page (ContentPage.razor.css), so
+   every page of the site shares one column under the header. Two cards still fit
+   side by side in it. */
+h1,
+article,
+p,
+.post-list {
+    max-width: 42rem;
+    margin-inline: auto;
+}
+
+/* The intro's last paragraph drops its margin (app.css), so the first card would
+   sit right under the text; this gives it the same air as between sections. */
+article {
+    margin-bottom: var(--space-5);
+}