The current form of the flag of Slovakia was adopted by Slovakia's Constitution, which came into force on September 3, 1992. The flag, in common with other Slavic nations, uses the white, blue and red colors.
Slovakia's flag in its current form (but with another seal on it or without any seal) can be dated back to the revolutionary year 1848 (see: The Revolutions of 1848 in the Habsburg areas). It was also used semi-officially in Czechoslovakia before World War II, by the Slovak Republic during WWII, and finally adopted (without the seal) on March 1, 1990, as the flag of the Slovak Republic within Czechoslovakia. The seal was added on September 3, 1992, and a special law describing the details of the flag followed in February 1993.
The blue triangle in the current flag of the Czech Republic, with which Slovakia formed Czechoslovakia up to the Dissolution of Czechoslovakia, was taken over from the blue strip of Slovakia's flag in 1920 into the flag of Czechoslovakia. The flag of Czechoslovakia was taken over by the Czech Republic in late 1992 in direct violation of the 1992 Act on the Division of Czechoslovakia explicitly forbidding state symbols to be used by the two successor states.