You can check the CSS and JS code coverage with Chrome Dev Tools:
You can show the Coverage tab from Dev Tools menu by choosing "More tools" => "Coverage".
Alternatively, to open Dev Tools press Cmd+Opt+I (Mac) or Control+Shift+I (Windows, Linux). After this, you can access the Coverage from the Command Menu: Cmd+Shift+P (Mac) or Ctrl+Shift+P (Windows, Linux) and then typing "Coverage".