Thumbnail Problem – Black Line

Hey guys

I’m quite new to wordpress so this might be a dumb question but I need help anyways: A black line appears at the side of my thumbnails and I don’t know how to remove it. When I decrease the size of my browser window the black line will disappear and when I increase the size it will get bigger. So I’m guessing it’s because the thumbnail is a set size and not “responsive”.

Does anyone know how to make the thumbnails “responsive” or to handle the problem some other way?

Thanks very much!

This is a screenshot of the problem:

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