Change the color of the line under a specific header

I want to change the color of the line under a SPECIFIC Header (h3). I know that I need go into a browser and find the ID for the specific header. I have done that:

The ID is "header_298", but I cannot seem to change the line color under that one. I have tried many different things, but the obvious one does not work:

#header_298 {

  border-color: red !important;

}

You should target the div (box) where the header is contained:

#cid_298 > div {

  border-color: red!important;

}

Here's the result: