Make controlbox headings bold

css/converse.css

@@ -9357,7 +9357,7 @@ readers do not read off random characters that represent icons */
   --controlbox-head-color-lighten-45-percent: #eff4f7;
   --controlbox-pane-background-color: white;
   --controlbox-heading-color: inherit;
-  --controlbox-heading-font-weight: normal;
+  --controlbox-heading-font-weight: bold;
   --chat-gutter: 0.5em;
   --minimized-chats-width: 130px;
   --mobile-chat-width: 100%;

sass/_variables.scss

@@ -80,7 +80,7 @@ $mobile_portrait_length: 480px !default;
     --controlbox-head-color-lighten-45-percent: #eff4f7; // lighten($light-blue, 45%)
     --controlbox-pane-background-color: white;
     --controlbox-heading-color: inherit;
-    --controlbox-heading-font-weight: normal;
+    --controlbox-heading-font-weight: bold;
 
     --chat-gutter: 0.5em;
     --minimized-chats-width: 130px;