Yes there was a typo error that Andi fixed, that was caused by copy and paste. Thank you.
So now when you install Arcade Basic, it should install the correct theme, not Able.
What method are you using to install the Arcade Basic template? Are you uploading it via FTP/WebDAV? Are you using the extension mananger? If so, are you searching and clicking install from the search results, uploading a zip file from your computer, or cloning from a URL? The theme worked for me when I tested it on my computer and on my website.
I checked style.ini and the required variable is defined in the file. I noticed there was an issue with installing the theme via the search results, that was caused by bad characters in the metadata and page and folder name (a space and a dash), so I removed the incompatible characters (which can also cause bugs and errors in other areas of dokuwiki, which is probably what's happening to you as it did me). It seems like templates are compiled or cached by dokuwiki before being executed, rather than being executed on the fly.
The changes I made to the template today should fix your problem. I suggest you delete the entire template from your website and install it again using the extension manager search result page. The fix I've just uploaded today, the entire thing would need being replaced rather than just changing one file.