Add space between each blog post on homepage

Hi,
I’m trying to add some spacing between each post title on the homepage and a thin line if possible. My site is: https://66.147.244.110/~susieric/construction/

I’ve added the following code to my CSS (child theme) but it doesn’t work. Can someone please tell me where I’m going wrong?

#home .recent-posts-4 {
margin-bottom: 40px;
}

Thanks.