Reduce padding above & below gallery blocks

Hi all, I want to reduce the padding between my single column and double column gallery grids, as they are currently set to a default that looks to be around 57px at full width (1440px - see attached screenshot). Ideally I want to reduce this padding to 20px top & bottom. 

I have found various custom CSS solutions on forums already and have tried the following but they haven't worked:

/* gallery padding */
.gallery-block {
    padding-top: 20px;
    padding-bottom: 20px;
}

/* gallery padding */
.gallery-block {
    padding-top: 20px !important;
    padding-bottom: 20px !important;
}

I managed to do it by editing each individual div within chrome's inspect tool (https://tppr.me/oRbaT) but can't seem to add the correct custom CSS to properly reduce the padding in Squarespace. 

Any suggestions you have would be much appreciated!!

Site link: https://www.laurenchalk.com/info-design
Password: apsleydrive

Hey @Ziggy absolute legend, thank you!