The 2nd Continental Congress ran from May 10, 1775, to March 2, 1789. The Journals of the Continental Congress are the records of the daily proceedings of the Congress.
From, Vol 8 (22 May - 2 Oct 1777), p 464; (cont.) proceedings of June 14, 1777.
"Resolved, That the flag of the thirteen United States be thirteen stripes, alternate red and white; that the union be thirteen stars, white in a blue field, representing a new constellation."
From, Public Laws Enacted During the First Session of the Eighty-First Congress of the United States of America, 3 Jan - 19 Oct 1949; Chapter 385.
"Resolved by the Senate and House of Representatives of the United States of America in Congress assembled, That the 14th day of June of each year is hereby designated as "Flag Day", and the President of the United States is authorized and requested to issue annually a proclamation calling upon officials of the Government to display the flag of the United States on all Government buildings on such day, and urging the people to observe the day as the anniversary of the adoption on June 14, 1777, by the Continental Congress of the Stars and Stripes as the official flag of the United States of America.
Approved August 3, 1949."
Happy Flag Day!