CSS

Hello,

If you want to create a new child theme, WordPress docs has this:
https://codex.wordpress.org/Child_Themes#Creating_a_Child_Theme_from_an_Unmodified_Parent_Theme

If you want to make some customizations to Supreme, we recommend the following:

CSS – Add CSS to the GeoDirectory Design Admin Panel called Scripts. Navigate to YourSite > GeoDirectory > Design > Scripts > Custom Style CSS Code
PHP – Add PHP Snippets to your site with the Code Snippets plugin, a Very lightweight plugin that makes it easy to manage your custom code, and keeps it all in one place even if your plugins or themes get updated.
https://wpgeodirectory.com/docs/customizing-your-style/

If you store your customizations in that way, then they will not be overwritten with updates of Supreme, allowing you to take advantage of updates.