Iconbox color

Hi

I have a page with three Iconboxes, each in a 1/3 section next to each other – all at the same page, in the same color section:
I would like to change the background color of each of the Iconboxes eg.: one red, one blue and one green (not icon background, but the background of the box itself).
I have tried using the folowing code to change the background:

#top .iconbox {
background: rgba(110, 128, 128, 0.49) !important;
}

.., but I cant get it to work.
Then I found the following code to also target each element:

#top .iconbox.avia-builder-el-5 {
background: rgba(110, 128, 128, 0.49) !important;
}

…, but couldn’t get it to work either.

Could you please help me target each of the icon boxes individually, and provide me with a quick CSS code to change the background color of each of these boxes.

If you need any information or clarification, please let me know.
I hope you can help me.

/Johnny