Plone 6 Classic - Theming Custom Styles

What is the expected default behaviour when css is added under "Theming" > "Advanced" > "Custom Styles"? Does the custom css affect only logged in users? Should it also affect anonymous users?

It seems that the custom.css stylesheet is not being served to anonymous users. I need to check to see if this is specific to our implementation or is a standard Plone 6 Classic "thing".