Theme submissions can be sent through email.
Simply attach the CSS file to the email, and include:
You can also submit your theme in a PR to the repository this is hosted at: roundabout-host.com/steve0greatness/ThemeIndex.
Simply place your theme CSS into a subdirectory under the theme direcotry(this should be your username), then include a bit of metadata in the themes.xml file in the project root.
This meta data should be as follows:
<theme>
<title>{Theme Name}</title>
<author
uri="https://{profile link}"
instance="{profile instance}"
username="{author username}"
>{Author display name}</author>
<uri>{pathto/theme.css}</uri>
</theme>