Good evening Ivaylo and welcome to the Events Calendar forum!
Thank you for your interest in our products.
We’ll be glad to answer your questions.
From the looks of it, this does not seem to come from our plugins. In fact, it does not look like the Events Calendar is on this specific site.
If I am mistaken, could you please share the link to our calendar on your website ?
With that in mind, try adding the following CSS rule to your style.css file or in your Custom CSS metabox: