Schengen countries are the current 26 states, you can enter any of them on a single Schengen visa. In addition, there is no internal passport control within the Schengen zone, which means that crossing the border of one country of the agreement, one can fly in the community without fail, without spending time, money and money to overcome bureaucratic red tape.

Both countries and Greece and Lithuania are included in the list of countries of the Schengen agreement, therefore, nothing prevents traveling to Lithuania on a Greek visa, the main thing is that the "first entry" rule is observed.

More details can be found on the page "Schengen visa".