‘Nothing found’ on home page after custom CSS edit

I agree with the comment of @the_hobbes about your code block inadvertently commenting out part of the theme’s code. If removing that part of the code doesn’t fix the issue, you can try reinstalling the WordPress theme. It will enable the homepage to display with the default CSS codes. Follow these steps:

  1. In the WordPress admin, head to Appearance > Themes. Activate
    TwentyFifteen.
  2. Click on your theme’s thumbnail. Then click the Delete link in
    the lower-right. Confirm delete.
  3. Head to Add New > Upload Theme. Install the zipped files of theme
    and activate it.

Now, you should be able to get access to your homepage.