How to configure ACLs that permit only established connections and deny all traffic sourced from the external network

Adding the established keyword at the end of access-list indicates that packets belong to an existing connection if the Transmission Control Protocol (TCP) datagram has the Acknowledgment (ACK) or Reset (RST) bit set.

access-list 110 permit tcp any any established

When you add this make sure you enable DNS otherwise the url will not able to use the Internet.