management server listener (#17)

Reviewed-on: #17
Co-authored-by: David Ashby <delta.mu.alpha@gmail.com>
Co-committed-by: David Ashby <delta.mu.alpha@gmail.com>

frontend/files/style.css

@@ -133,6 +133,10 @@ body {
   overflow: hidden;
 }
 
+.hidden {
+  display: none;
+}
+
 #header {
   height: 30px;
   width: calc(100vw - 20px);