UI: Tweak style of header messages

templates/default-layout.cassius

@@ -116,3 +116,10 @@ input:hover[type="submit"]
 
 .username
     font-weight: bold
+
+.message
+    padding:       1rem
+    margin:        4rem 3rem 4rem 4rem
+    border:        none
+    border-radius: 0.5rem
+    background:    #{dark main}

templates/default-layout.hamlet

@@ -82,7 +82,7 @@ $# <http://creativecommons.org/publicdomain/zero/1.0/>.
 
   ^{breadcrumbsW}
 
-  <div #messages>
+<div #messages>
   $forall (_status, msg) <- msgs
     <div .message>#{msg}