I have created a new page which has TT post category element with the latest post of one category. I have attached you a screenshot in order to see that there is a bottom border at the end of each post that continues at the sidebar area.
It seems like the wrapper of the posts covers the sidebar area. If you want to see the page live is at https://sindimotes.com/deltia-tipou/
I will also want to ask if it is possible to hide the author of the posts.