Change text to bold on hover over other elements

Hey guys,

I hope someone can help me. I got 4 Headlines on my site, which show different texts next to themselves if you hover over them. Probably terribly executed, I got lost in my grids, but it works :smiley:

The headlines are changing to bold on hover, now I would like to make the first headline also bold, to indicate there is an interaction. But when I hover on the other ones, the first one should go back to normal. Any Idea how to solve this?

Thank you!

Here is my public share link: