Christianity/Morals

I have a question for atheists, Christians believe morals come from God, that’s the foundation and written in the bible it says

”I will put my law in their inward parts, and write it in their hearts” Jeremiah 31:33

“For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves:

Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another Romans 2:14–15 (KJV)

How do athiests establish and measure morality with limits without God? This doesn’t make any sense to me, wouldn’t it just be based on feelings and what you think is correct, we can see the morals of people change overtime very evident allowing things that aren’t to be legal yet the word of God is consistent. I don’t believe you can be fully moral if you don’t have the Lord, theres no basis or foundation for it.