[MM-63586] Fix Jump to recents dismiss icon visibility (#30581)

- Fixed dismiss icon color in the Jump to recents toast by changing the fill from button-bg-rgb to button-color-rgb
- Added hover state for dismiss icon to increase visibility when hovered

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <noreply@anthropic.com>

webapp/channels/src/components/scroll_to_bottom_toast/scroll_to_bottom_toast.scss

@@ -50,13 +50,17 @@
 
         svg {
             padding-top: 1px; // To align vertically
-            fill: rgba(var(--button-bg-rgb), 0.64);
+            fill: rgba(var(--button-color-rgb), 0.64);
             vertical-align: middle;
         }
 
         .close-btn {
             cursor: pointer;
             line-height: normal;
+            
+            &:hover {
+                fill: var(--button-color);
+            }
         }
     }
 }