Need help with Page Sections

I see. Try this CSS:

.site-footer {
    margin-top: 20px;
}

To add white border around specific sections:
- First add the class whiteborder in Custom Classes field in the Sections settings
https://docs.generatepress.com/article/sections-overview/#opening-the-section-settings

- Then add this CSS:

.whiteborder{
    border: 2px solid #ffffff;
    box-sizing: border-box;
}