change space between portfolio thumbnails

Hey, I want to change the space between my portfolio thumbnails.

Entering

.portfolio-thumbnail {
padding-top: 40px;
}

like I read in another thread does not work for me.

I have installed Jetpack and tried to change it with this code before:

.col-xs-1, .col-sm-1, .col-md-1, .col-lg-1, .col-xs-2, .col-sm-2, .col-md-2, .col-lg-2, .col-xs-3, .col-sm-3, .col-md-3, .col-lg-3, .col-xs-4, .col-sm-4, .col-md-4, .col-lg-4, .col-xs-5, .col-sm-5, .col-md-5, .col-lg-5, .col-xs-6, .col-sm-6, .col-md-6, .col-lg-6, .col-xs-7, .col-sm-7, .col-md-7, .col-lg-7, .col-xs-8, .col-sm-8, .col-md-8, .col-lg-8, .col-xs-9, .col-sm-9, .col-md-9, .col-lg-9, .col-xs-10, .col-sm-10, .col-md-10, .col-lg-10, .col-xs-11, .col-sm-11, .col-md-11, .col-lg-11, .col-xs-12, .col-sm-12, .col-md-12, .col-lg-12 {
position: relative;
min-height: 1px;
padding-right: 8px;
padding-left: 8px;

But this does not effect the space between the rows only the space between the columns.
(If I add padding top it only changes the space from header to top menu)
How can I change the space between the rows?

This is my website:
https://redloondesign.com

Thanks!

Best wishes, Ando