Web design is actually written like this in Ukrainian: "веб-дизайн" (with a hyphen)
"Web design - my hobby" seems like a more than adequate translation with at most a warning.
I don't think English is much known for sentences like "I Tom" or "Life not bed of roses".
In English, if we use a dash then leaving out "is" would be the best interpretation, in my experience. Is it different in Ukrainian?