fixed scrollbar size and split focus

src/widgets/notebook.hpp

@@ -59,11 +59,17 @@ private:
     struct Item {
         NotebookTab *tab;
         QWidget *page;
+        QWidget *selectedWidget = nullptr;
     };
 
     QList<Item> items;
     QWidget *selectedPage = nullptr;
 
+    bool containsPage(QWidget *page);
+    Item &findItem(QWidget *page);
+
+    static bool containsChild(const QObject *obj, const QObject *child);
+
     NotebookButton addButton;
     std::vector<NotebookButton *> customButtons;