Center 404 correctly

borgweb/borg/templates/404.html

@@ -3,29 +3,28 @@
 
 {% block title %}404: Not Found{% endblock %}
 
-{% block script %}
-{% endblock %}
-
 {% block style %}
-html, body {
-            height: 80%;
+        body {
+            background-color: aliceblue;
         }
 
-        main {
+        .vertical-center {
+            min-height: 80%;
+            min-height: 80vh;
+
             display: flex;
             align-items: center;
-            background-color: aliceblue;
-            text-align: center;
         }
 {% endblock %}
 
 {% block body %}
 
-<main class="form-signin mx-auto w-25 px-5">
-    <div class="mx-5">
-    <h1 class="h1">404: Page Not Found</h1>
-    </div>
-</main>
+<div class="container vertical-center">
+  <div class="row w-100">
+      <h1 class="text-center display-1">404: Not Found</h1>
+  </div>
+</div>
+
 
 {% endblock %}