Featured image / thumbnail can not be hidden from posts/categories

So the problem with using someone else’s CSS is that you don’t know if they are using a theme which has the same class names for the different web elements as your theme. Here’s what you want to use:

.single .featured-media,
.category .featured-media {
    display: none;
}

This worked, thank you so much!

I think this is the issue I’m having but would like to clarify. Any image I select as featured in Hemingway Rewritten becomes the header image.

I would like to be able to select a feature image for my posts without altering the header image.

How would I do that and in what file?

Thank you!

This The Same happening

As a function I do this ?
Should I where I place the code?

Thank you!