Tweak the subtitle of private chats' headings

css/converse.css

@@ -7339,9 +7339,8 @@ body.reset {
     flex-direction: row-reverse;
     padding: 0; }
   #conversejs .chat-head .user-custom-message {
-    color: white;
+    color: #e7f7ee;
     font-size: 75%;
-    font-style: italic;
     overflow: hidden;
     text-overflow: ellipsis;
     white-space: nowrap;
@@ -7702,7 +7701,7 @@ body.reset {
   font-size: 20px;
   padding: 0; }
   #conversejs.converse-fullscreen .chat-head .user-custom-message {
-    font-size: 50%;
+    font-size: 70%;
     height: auto;
     line-height: 16px; }
   #conversejs.converse-fullscreen .chat-head .chatbox-title {

sass/_chatbox.scss

@@ -65,9 +65,8 @@
         }
 
         .user-custom-message {
-            color: white;
+            color: lighten($chat-head-color, 50%);
             font-size: 75%;
-            font-style: italic;
             overflow: hidden;
             text-overflow: ellipsis;
             white-space: nowrap;
@@ -552,7 +551,7 @@
         font-size: $font-size-huge;
         padding: 0;
         .user-custom-message {
-            font-size: 50%;
+            font-size: 70%;
             height: auto;
             line-height: $line-height;
         }