Recent post text not centered and transpartent

first of all i’m not a programmer and zero experience with css.

i use recent posts for my slides with a background, text of the slides is not centered and transparent (issue probably occured after the plugin was updated).

i saw another question here of someone who needed help with almost the same issue and probably i can correct the issue in the css.
first of all i need to know which file i need to edit and which section of that file.

hope someone can point me in the right direction.

regards,

rene

The page I need help with: [log in to see the link]