I need help understanding my new Roth contributions.

I recently opened up a 401k through my company’s plan. Because I live with my parents, don’t have many bills, and have a good amount of regular savings, I’ve decided to max out my contributions in order to catch my retirement savings up. I’m just a bit confused about the cost breakdown of my check and was wondering if anyone could explain it to me.

Let’s say my weekly paycheck is $1077. Normally, I would take home $850 after taxes but with my new 401k contributions (6% pre-tax, 59% Roth basic), it is now only $166. That means I only get like 15% of my pre-tax check (20% of my post-tax). Here is the full cost breakdown of my check (rounded to the nearest dollar):

Total = ~$1077
401k Roth - $635
401k Pretax - $65
Federal Withholding - $78
Social Security Tax - $66
State Tax - $35
Vacation Purchase - $17 (bought an extra week in advance)
Medicare - $15
Take-Home = ~$166

Can anyone help me understand where the 6% and 59% difference comes into play and why it seems like the Roth basic is also coming out of my check as pretax (when Fidelity says it should be post-tax)?