Accusative at the begging of a sentence.
I know that the case Accusative goes with the questions wen? und was?
But I don't understand why this sentence starts with accusative "Lieben"
" Lieben Gruß zum Frauentag! "
Vielen Dank alle
It's not an actual sentence, it's lacking the verb. In fact, it's shortened from "Ich schicke/sende Dir/Ihnen einen lieben Gruß zum Frauentag" or similar. Most greetings are written in this short form, especially at the end of a message. But apart from that it's not a problem to start a sentence with an object in German, e.g. "Einen schönen Frauentag wünsche ich Dir".