Add wiki replacement warning

Author: PTKay

hedgedocs/web/overrides/main.html

@@ -18,6 +18,9 @@
   <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.6.1/jquery.min.js"></script>
 {% endblock %}
 
+{% block announce %}
+ANNOUNCEMENT: HedgeDocs will soon be replaced with a wiki version! However, for a limited time, both versions can be accessed, with the wiki being available <a href="https://wiki.hedgedocs.com">here</a>.
+{% endblock %}
 
 {% block content %}
   <div class="imagePreview">

hedgedocs/web/stylesheets/extra.css

@@ -36,7 +36,10 @@ body {
 }
 
 .md-banner {
-    background-color: #b71c1c;
+    text-align: center;
+    font-weight: bold;
+    color: #FFFFFF;
+    background-color: #820000;
 }
 
 .md-copyright {

hedgedocs/web/stylesheets/ultradark.css

@@ -32,6 +32,11 @@
     --ultradark-anchor-link-color: #0074ff;
 }
 
+[data-md-color-scheme='ultradark'] .md-banner {
+    background-color: #cbcbcb;
+    color: #000000;
+}
+
 [data-md-color-scheme='ultradark'] .contributor {
     color: var(--md-default-fg-color);
     word-break: break-word;