Why a candle brought near the mouth of a jar containing hydrogen gas starts burning but is extinguished when pushed inside the jar?

When the candle is brought near the mouth of the jar containing hydrogen gas, the hydrogen gas reacts with oxygen in the air to produce water vapor and heat, allowing the candle to burn. However, when the candle is pushed inside the jar, the available oxygen is quickly used up by the candle flame, leading to oxygen depletion and eventual extinguishment of the flame.