message_ui: Show non-sticky recipient bar action buttons on hover.

- Toggles the CSS rule `visibility: hidden;` on the recipient bar
  controls when the bar is hovered.
- If the recipient bar is sticky, then the controls are always visible.
- In case of conversation views, the recipient actions remain visible.

Fixes part of #26852.

Co-authored by: ecxtacy <dc.dhruvchouhan@gmail.com>

web/styles/message_header.css

@@ -75,6 +75,23 @@
                 top: -0.5px;
             }
         }
+
+        .recipient_bar_controls {
+            visibility: hidden;
+        }
+
+        /* Show the bar controls on hover and when the bar is sticky */
+        &:hover {
+            .recipient_bar_controls {
+                visibility: visible;
+            }
+        }
+
+        &.sticky_header {
+            .recipient_bar_controls {
+                visibility: visible;
+            }
+        }
     }
 }
 

web/styles/zulip.css

@@ -887,6 +887,13 @@ div.focused-message-list {
     display: block;
 }
 
+/* In conversation view, always show the recipient bar action buttons */
+div.focused-message-list.is-conversation-view .recipient_row {
+    & .recipient_bar_controls {
+        visibility: visible;
+    }
+}
+
 .rtl {
     direction: rtl;
 }