Question

How/Why does a matchstick fire burn against gravity

Answer 1

When a match stick burns on Earth it heat the surrounding atmosphere, which cause the air to expand and air become less dense. The gravity pull draws the colder and more dense air down to the flame ase, the hot air got displaced, which rises.

Hope this will make you satisfied.

;)

Answer 2

When a match stick or any other fuel for fire burns it creates low pressure area around itself. This results in form of rise of flame into upward direction as atmosphere.

Well this is all I know.