Can anyone explain 401k limits from the employee and employer standpoint?

Say one makes 250k and company gives 15% DC and Employee puts 10% for the 401k. So employee math shows 25k and the company gives 37.5k for the year.

Where does the 18.5k and 55k limits come in?

Is 18.5k the max limit on the employee, so in this case you can put in 10% but as soon as you hit 18.5k your paycheck will no longer deduct towards the 401k?


And what case does "cash over cap" happen?