Hi Paul,
1. Yes this is the right location to place custom CSS code. However, I can’t seem to verify that the code has indeed been added while viewing your site from my end. There may be a caching mechanism set in your website that’s causing this.
May you kindly clear any caching mechanisms set in your website whether it be from your CDN(cloudflare), hosting provider or any plugins?
2. Yes, there is, and I can see that you’ve already added them. In any case, here is our article with regards to this: https://docs.generatepress.com/article/smooth-scroll/
so as long as we set this page jumpe in one page or different pages, it should not add extra css code to adjust the position whatever i use sticky navigation or not.
Adding the CSS through Additional CSS will apply the code for all pages in your website.
If you wish to apply it to specific pages only, then a plugin like Simple CSS would be the key to do this: https://docs.generatepress.com/article/adding-css/#simple-css
However, these small lines of CSS code in Additional CSS should have almost no effect to the loading speed of your website.
one more thing, if Deactivating sticky navigation, i still need the extra css code from you?
The Sticky Navigation can be disabled through Appearance > Customize > Layout > Sticky Navigation.
Here is a document you may refer to regarding this: https://docs.generatepress.com/article/sticky-navigation/
If you wish to deactivate the Sticky Navigation page specific, then yes, we can also provide custom code for this to you.
Hope this clarifies. 🙂