Files with .sublime-theme extension are Sublime Text theme files. Sublime Text comes with a default theme. You can access the default theme by selecting Preferences -> Browse Packages. For color combinations, Sublime Text uses the .tmtheme extension.
To open a .sublime-theme file, install Sublime Text. If Sublime Text is installed but doesn’t open .sublime-theme files by default, right-click on the file and choose “Open with”. Then select Sublime Text and check “Always use this app”.
If you cannot open a .sublime-theme file, reasons may include: no installed program supports the file type; the file is damaged; the file is incorrectly linked in the registry; the Sublime Text installation is incomplete; the file is infected; the drivers are outdated; your computer lacks the resources to open the file.
Programs that can open .sublime-theme files include Sublime Text on Windows. After installing Sublime Text, the system usually automatically associates .sublime-theme files with it. If not, select Sublime Text as the program to always open .sublime-theme files.
The .sublime-theme format was developed by Sublime HQ Pty Ltd and is likely generated by Sublime Text. It contains interface appearance information like button placement and font size in JSON format. Theme authors can define settings for users to tweak themes.