Fix z-index ordering btw cell title toolbar and below cell toolbar

Fix #104163

src/vs/workbench/contrib/notebook/browser/media/notebook.css

@@ -498,7 +498,7 @@
 	position: absolute;
 	display: flex;
 	justify-content: center;
-	z-index: 30; /* over the focus outline on the editor */
+	z-index: 25; /* over the focus outline on the editor, below the title toolbar */
 	width: 100%;
 	opacity: 0;
 	transition: opacity 0.2s ease-in-out;