Click sharing. Then copy the Style Sheet. (This is already parsed for DeviantART)
Save as a .txt file.
Submit to DeviantART as an installable skin.
DeviantART Related > DeviantART Skins & Scripts > Journal & Gallery Skins > Installable Journal Skins
Write a description about use, any special DIVs, characters, etc. Add a link to your live preview so users can see it before installing.
(If you're part of any groups and want to show it off, submit to groups #deviantCSS
If you have any particular rules, etc link or list them.
You'll upload your txt file as well as a preview image. Use the screenshot. I do few edits in order to show off how it actually looks, but that's up to you how you present it. The live view will allow them to view the functionality.
On submit, it will ask you to upload your images. Make sure to select the correct ones for each choice.
Once everything is uploaded, the install button should appear. Click it to install to your own journal, this will give you a thumbnail in your sidebar. Then write a new journal!