How do I reduce the padding inside these containers?

Hi there,

If possible, without affecting the container padding on my single blog posts.

Since you are removing the padding for the featured images, it would actually be easier to set the padding you want for those blocks in the customizer, then we can target the single post content padding separately like this:

body.single.separate-containers .inside-article {
    padding: 20px;
}

Adding CSS: https://docs.generatepress.com/article/adding-css/

Great, thanks Leo!

No problem :)