How can I get rid of the two gray balks (above, in the image not shown), below (in the image with caption text)?

I saved an example on my web-site:
http://www.christener.ch/wp-content/uploads/2016/12/balks-problem.png

I am looking around for a solution since hours, nothing found. But I am sure it must be something simple. If it needs some CSS to do, do you now someone who could do this?

Thank you for your help?