Style account switcher to match the current theme (#4817)

src/widgets/AccountSwitchPopup.hpp

@@ -21,6 +21,8 @@ protected:
     void focusOutEvent(QFocusEvent *event) final;
     void paintEvent(QPaintEvent *event) override;
 
+    void themeChangedEvent() override;
+
 private:
     struct {
         AccountSwitchWidget *accountSwitchWidget = nullptr;