Zobacz przywitanie
Importing the demo .xml file is only a first step when achieving a demo look. You have to set up your menus under Appearance / Menus, edit widgets and sidebars under Appearance / Widgets and set up your front page and blog page.
Probably the most important step is to set the demo front page (page with title Knowledge Base. Elegant. Lightweight. WordPress Based.) as your site's front page. It can be done under Settings / Reading. Then you can fine tune it under Appearance / Customize / Default Front Page Settings.
There is a separate article about the front page. You should definitely read it.