How to find formed class in body?

Question

WordPress

Hello, I'm sorry for the incomprehensible question in the topic, I do not know how to write correctly. Just started learning CSS, practicing with Wordpress. So, I installed the theme, the buddypress plugin and the RTMedia media extension to it, so that users can add photos / audio ...
But it's bad luck, when you go to the MEDIA tab (on a user or group page), the site slides down from the top and scrolling is turned off on the page. Having examined the element from above (empty space), I found that in the body if one of the classes is removed (via F12), namely media, then everything starts to work normally. The question is how to find it and remove it in the code? Where is it formed?
Screenshot:
https://yadi.sk/i/7iAGDpKmmBYYM
Examples:
It's ok here: water.pe.hu/gruppy/derevolaz
Here's a jamb:water.pe.hu/gruppy/derevolaz/media

Answer 1

all information at your fingertips. css file names are here / the path is displayed when you hover the mouse
and here is your picture :
the red arrow is the file :)