Increase Icon size from Icon Boxes only on specific pages

Hello,
Need some help please, kind of stuck and I see no solution atm.
I want to increase the size of the icon from an icon box.
Using this css, everything works fine, but it’s obviosuly modifying all the icons from all icon boxes, for every page:

/*Icon Box Increased Icon size*/
#top .iconbox_left_content .iconbox_icon{
height: 30px;
line-height: 50px;
font-size: 80px;
}
.iconbox_left_content .iconbox_content {
font-size:30px;
}

I just want to increase the icons only on some pages. I have modified the functions.php, in order to turn on custom css classes, but even if I assign a class to an icon box, it modifies the text, not the icon.

I used this code:

.bigIconBox{
height: 30px;
line-height: 50px;
font-size: 80px;
}

Thank you.
Best regards,
Marius.