I have a client using SharePoint Online that I have developed a custom theme and custom stylesheet for. The goal is to have the styles and theme applied to the root site, subsites, and be provisioned for any newly created sites. I am trying to stick with the best practices of not using custom master pages or the feature framework as I want my client's solution to be stable for them in the long term with minimal maintenance.
I do not have the ability to use a provider hosted app as they do not have the resources for additional server space to run it. This has ruled out the use of remote provisioning or many of the available Office Dev PnP solutions.
I have attempted to use a SharePoint hosted app to apply the custom pieces but it is unable to act on the web provisioned event so I am unable to apply the customizations to newly created sites.
I have also attempted to use Alternate CSS URL's for the stylesheet but this only applies to subsites when manually selected to do so and it does not automatically apply to new sites.
I have been researching and thinking of potential ways provision the branding given my constraints but I can't come up with a viable solution.
Any help you can offer would be greatly appreciated, thanks!