v8.1.30
I created the same extremely basic css files within the root ../themes/ folder, which simply imports the light.css file, one called "test-light.css" and another called "test-asm-light.css". The "test-light" appears in the designer theme list but the "test-asm-light" doesn't. I've waited the 5mins gw file update time, i've called the system.project.update() function (from Ignition Extensions) to force update from file changes, but I've also had our actual theme with 2 dashes sitting in there for days, and it never shows up.
If I replace 1 of the 2 dashes with an underscore, it shows up.
E.g.
Works:
test-light.css
test_asm-light.css
Doesn't work:
test-asm-light.css