Think a collection of networks subnets is 255.255.65.0 and 192.168.23.12 is an IP address of a device that are in that network. How to find the network portion and host portion of that IP address?

Normally we used subnets like 255.255.255.0, 255.255.0.0, 255.0.0.0 in class C, class B & class A in order. When we want to find the network & host ids of an IP address, we are looking at 1’s & 0’s of that IP address and find the network & host portions or with the help of CIDR value. What happens if a subnet of a network is address like 255.255.65.0? How to find that type of subnet’s network & host portions?