We're limited in what we can say by the few lines of logs that contain somewhat limited info. However, the first set of logs is probably nothing more than the usual port scans and sweeps where attacker's and malicious code like worms are scanning the Internet looking for hosts to infect.
I'm not sure what service listens on TCP port 3450. And according to Dshield it doesn't seem to be commonly targeted. »
www.dshield.org/port.htm ··· ort=3450 Dshield also says both those IPs are from Germany. Why two different hosts from Germany would be trying to connect to you on TCP port 3450, at around the same time, I don't know. Whatever it was, it was blocked by your firewall so it can't hurt you.
As for the outbound traffic that was blocked in your second set of logs, your computer 192.168.1.65 tried to connect to 198.145.250.87 on TCP port 8888 which was blocked by your firewall so your computer then tried again a while later, which is why you see the log entry repeated.
Maybe that connection had something to do with CSS, I don't know. You need to figure out what program was responsible for it by typing netstat -bano in a command prompt. It may require admin privileges depending on what version of Windows you're using. You could also use TCPView »
technet.microsoft.com/en ··· 437.aspx however you will only find out what program is responsible for that log entry if that program is currently trying to use the network.