Very bad in explanation but my try (did not open photoshopn PC sucks so hard that its gonna take 5 minutes to open and its gonna cut my music and bug the browser) so i will try without PS opened
I say :
- rounded rectangle (for radius, as CMAIN probably 10 or 15px)
- gradient color at 80° start by white - primary color (black or violet as in the pic) - white (make sure the white is very small so there is just a lighting effect to it.
- inner shadow (change the angle so its on top, around 3px or 4) put the color white to the shadow, play around with the opacity.
If you have PS... it can be done just by playing around :/ nothing really hard :/