Title 36, United States Code, Section 112 (Public Law 105-225) declares this Honor America Days. The 21-days between Flag day and Independence Day are days in which:
Congress declares that there be public gatherings and activities during that period at which the people of the United States can celebrate and honor their country in an appropriate way.
President’s have simply mentioned in the Flag Day proclamations such as that by Barrack Obama on June 12.