Conditionally Fill a Cell Based on Row/Cell Count

I am trying to conditionally fill/highlight a cell in column A, based on the number of rows to count to get to it...

For example:

Adding to a cell just adds to the cell's value, so it's likely it's some kind of add-to-row-count kind of function? Anyone have any suggestions on how to go about accomplishing this?

Thank you,
Kristine