We do not currently know of any antonyms for code-behind.
The noun code-behind is defined as:
A technique in object-oriented programming in which the visual and back-endsource code are stored in separate files, allowing designers and programmers to work independently. Code-behind is a technique used in Microsoft programming platforms, including ASP.NET and XAML, where the practice is facilitated by separating the visual and code aspects through the use of partial classes.