Hello Tracker,
We have a very good news for you, now you don’t need any custom CSS for hiding featured image in the single post. You can hide feature image in single post by going to the Appearance=> Customize => Single Post Options , You will see there Single Post Layout ( Image display options ), there are 3 options
- Left Image
- Large Image
- No Image
Select No Image for hiding featured image. Hope this will solve your issues.
Further the next image displaying is not featured image in your site, it is image using in the content.
Best Regards,
Acme Themes