Themes are manually added to the themes page on Fedilab's website :)
You're the one who posted about a solarized light theme, right?
If you can, open an issue in Fedilab's repo and attach your exported theme there
Or upload it to a service like https://framadrop.org. Then share the link here on Mastodon
Server run by the main developers of the project It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!