add css adaptions for simplesamlphp pages

Adapt css for new Simplesamlphp version 1.18+

css/Login-Form-Clean.css

@@ -66,3 +66,12 @@
   text-decoration: none;
 }
 
+#homepage{
+        position:relative !important;
+}
+
+#header{
+        background: none;
+        height: fit-content;
+}
+