Global Style CSS

Hi Ian,

If by "Global style" you meant global styling from the theme's customizer settings, the only global styling the customizer has would be the colors. https://generatepress.com/generatepress-3-1-global-colors-dynamic-typography/

To be honest, in a sense, everything in customizer settings can be considered "global" as the settings here are general application to all pages and posts.

select a caption for all images on the site and give it some padding.

For this one specifically, you'll need a custom CSS.

Example:

figure.wp-block-image figcaption {
    padding: 20px;
}