formatting row color by date

I created a report for people enrolled in service requests.

So I have a Submit_Date column.

Now I want to see the final report such that the rows with:

1)Submit_Date from 1-10 days ago are green

2)Submit_Date from 11-20 days ago are yellow

3)Submit_Date from 21-30 days ago are red

4)and rest everything is not formatted or No-Color...

Also I have one additional question; I see that the data-type of Submit_Date is "datetime"

So would I be using Today() as the reference point or Now() as the reference point?

Dhananjay Rele