Fix microsoft#184434. Remove bg gap between selected cells (microsoft#184436)

Author: rebornix

src/vs/workbench/contrib/notebook/browser/notebookEditorWidget.ts

@@ -802,6 +802,13 @@ export class NotebookEditorWidget extends Disposable implements INotebookEditorD
 		styleSheets.push(`.notebookOverlay .monaco-list .monaco-list-row .cell-focus-indicator-bottom { height: ${cellBottomMargin}px; }`);
 		styleSheets.push(`.notebookOverlay .monaco-list .monaco-list-row .cell-shadow-container-bottom { top: ${cellBottomMargin}px; }`);
 
+		styleSheets.push(`
+			.notebookOverlay .monaco-list .monaco-list-row:has(+ .monaco-list-row.selected) .cell-focus-indicator-bottom {
+				height: ${bottomToolbarGap + cellBottomMargin}px;
+			}
+		`);
+
+
 		styleSheets.push(`
 			.monaco-workbench .notebookOverlay > .cell-list-container > .monaco-list > .monaco-scrollable-element > .monaco-list-rows > .monaco-list-row .input-collapse-container .cell-collapse-preview {
 				line-height: ${collapsedIndicatorHeight}px;