Conditional Formatting Header Rows with Blank Sub Rows Below Alternating Group Colors

Have orders with multiple line items. The first line of the order contains the order number in column A, and all lines below inside that order are blank in column A.

I want the first order row and all its associated sub rows to be white, with the second order and all its associated sub rows being gray.

[Screenshot here shows how my sheet is structured.]

Thanks in advance!