In the same region how does the ec2 of account A access the lightsail server of account B from inside and outside

To access the Lightsail server of account B from inside the EC2 instance of account A, you can use the private IP address of the Lightsail server. You would need to ensure that the security group associated with the Lightsail server allows inbound traffic from the security group associated with the EC2 instance.

To access the Lightsail server from outside, you can use the public IP address or domain name of the server. You would need to ensure that the security group associated with the Lightsail server allows inbound traffic from the internet. Additionally, you may need to configure network ACLs and routing tables to allow traffic to flow between the two accounts