What Taxes Count toward the 100%/110% rule for underwithholding?

[rss7993]

Trying to make sure I won't be subject to a penalty for underwithholding. When trying to figure out how much I need to withhold, it is 100%/110% of only federal income taxes, not social security or medicare, correct? Put another way, is it A or B:

A: 2020 federal income taxes withheld must be 110% more than 2019 federal income taxes.

or

B: Add together 2020 federal income taxes withheld, social security, and medicare. This number must be 110% of 2019 federal income taxes, social security, and medicare.

Thanks!

[ee-ea]

A: 2020 federal income taxes withheld must be 110% more than 2019 federal income taxes.