A customisation of the “Simplified Dark” theme that ships with Textual (originally by Ben Alman). The idea was to re-tool it towards some more relaxed and “earthier” colours, in addition to switching the theme to Helvetica.
Screenshot:
Click the image for a full-sized version.
Download
Instructions: Unzip the file, and place in your “~/Library/Application Support/Textual/Styles folder”.