Animated Number Counter - Where does the black frame come from?

Hello, I was unsure in which area I can ask my question. Iโ€™ll give it a try here. (If itโ€™s wrong, please move it). I have created one with the Animated Number Counter and integrated the code on two pages as a test. On one page everything looks fine. But on the other page (both pages are created with Wordpress) there are black frames around the tiles of the counter (which then disappear on mouseover). I canโ€™t explain where these frames come from. Does anyone have an idea where I could look? In the advanced settings in the widget, the frame is set to transparent.

Hey @aki is there anywhere we can see the issue live? That would be extremely helpful.