changed padding to pixels, fixes #9916 (#9924)

public/sass/components/_panel_graph.scss

@@ -280,7 +280,7 @@
 
   .graph-annotation__header {
     background-color: $popover-border-color;
-    padding: 0.40rem 0.65rem;
+    padding: 6px 10px;
     display: flex;
   }