What will the following year tax burden be on partial repay of an premature 401K withdrawal?

What will the following year tax burden be on partial repay of an premature 401K withdrawal?

I quit my job.
I have a 401K from the previous employer — and took out a partial money due to COVID hardship — 401K is still active.

If I withdraw — $90,000 on December 2020 — then during tax season 2020 and before filing my 2020 taxes — I repay $30,000 — what will the tax burden be?
Will it be the full $90,000 or $60,000?

Thanks!