This code snippet goes into the child theme style.css file. You can adjust the pixel number from 20 if you like to increase or decrease the gap distance between homepage posts.
Alternatively, you can add a border between the posts as well. That pixel number on the border thickness can be adjusted along with the border style (dashed) and the color if you wish.
/* Adjust Gap Between Posts On Homepage */
.home article {
margin-bottom: 20px !important;
border-bottom: 2px solid grey;
}