Just say no.

 

Typically the rear of a rear wheel drive car is wider than the front. The few mm up front should make the wheel setup more "square".

 

Will the carbon fenders also be wide body? If so, yeah go for it, why not? And since your car is black, the carbon blends in anyway.

 

there isnt any that are carbon wide body the ones im looking at only stick out 10mm apparently but i love the style and look so thats why i wanted to like keep the front with those but get the kit for the back. i have a feeling it might look retarded. i love carbon on black cars!!

 

It's your car so you can do whatever you want if you like the look. I'm sure if it's done tastefully and done well it will look good.
What you're describing makes me think of certain race cars over the years. Maybe hillclimb cars. Or even 1970s/1980s Porsche race cars.

How much wider will the rear be vs the front?

 

yea youre right ive seens tons of them that look really good with the full kit on but its a 70mm difference from the front fenders i want to the back wide body kit.

 

If you get the carbon front fenders and they are +10mm, and you get the back widebody fenders that are +70, I think it will/can still work just fine, especially on a dark car. It's a difference of 60mm, which is 2.36 inches. I don't think it will be noticeable. As long as you have the right wheel fitment, anything can work.