brake lights on 2007 Elantra wont go off even when car is shut off.

That's your brake lights staying on. Check the brake light switch,either it has failed or the stop is broken,look under dash,drivers side above the pedal,less than $15.00 for a new switch,local parts store.Google Part Number: JA4371 for a picture....

See any small pieces of broken black plastic in drivers floor board? As mentioned in other answer .. Common problem for this vehicle is broken brake light switch *stop pad*..