Grid Row: Specific Border

Hello,

i’m trying to get a right border to my grid row element.
My grid got the following class set: grid_border_right

This is my css i did paste in the quick css:

/* Border für Grids */
.grid_border_right {
  border-right: 5px solid #FFFFFF !important;
}

Unfortunately i can’t create a border this way. Does somebody know what i’m doing wrong?
Link to the page can be find below.

Thanks,
Dennis