Any reason behind the darkness on my screen?

I just got finished modding this thing (switched battery and hard drive) and I just only noticed the darkness around the screen at the bottom. Is it a reason for concern? Ipod 7th Gen

Modifications: 3000 mah thin battery Quad iflash board

I just got finished modding this thing (switched battery and hard drive) and I just only noticed the darkness around the screen at the bottom. Is it a reason for concern? Ipod 7th Gen

Modifications: 3000 mah thin battery Quad iflash board