Removal thumbnail Project page

Hello,

At the portfolio page you show off the projects you done. Once you click a project, it opens the project page more into detail. There it shows off the image thumbnail, but only half of it and I cannot make it appear correctly and bigger.

How do I remove the thumbnail on top? When I select inspect element, i get to see the following code.

img.attachment-entry_with_sidebar.wp-post-image {
}

So I add:

Display: none;

But it doesn’t work, I tried to add various versions of the page thumb displaying… but on the live coding of the css… it just doesn’t go away.

Is there a way to remove this?

With kind regards,

Rowan