i was wondering if its safe to do cardio after leg days or is that pushing it too much.
I do it.
However, my cardio after leg day is usually around the 70% of max heart rate for ~45 minutes, which probably puts me more in the fat burning zone than the cardio zone. Also, I try to maximize the amount of time between the two. I do legs early in the AM and cardio late in the PM on the following day.
Why wouldn't it be safe?
I do it. I even try sprints sometimes but obviously about the best I can do is a quick jog.
Unless you're still so fatigued there's a chance you're going to trip and do an ankle or so tight you'll pull a hammy, you should be okay.
Make sure to warm up well first if you're worried.