Is there any reason why my federal tax is reduced while the state tax remained almost the same?

I’m a PhD student living in South Carolina. I have a graduate research assistant job in my university and my salary is $20,000 per year. I just got my paycheck recently and I realized that my direct deposit is increased about $62 this time in comparison to previous paycheck. In fact, each two weeks I received direct deposit of $714.31 but this time which covers the dates 12/16/2020 to 12/31/2020 I received $776.86.

I checked the details and realized that in previous paychecks I paid:

• Federal tax: $91.77
• State tax: $27.25

But this time on my recent paycheck it is:

• Federal tax: $31.04
• State tax: $25.43

Did something happen to tax rates recently that I missed probably? My question: Is there any reason why my federal tax is reduced while the state tax remained almost the same?