If you remove the class right now the header reverts to how it was. This is what these extensions are doing right now, simply removing a class. I'm saying that

If you remove the class right now the header reverts to how it was. This is what these extensions are doing right now, simply removing a class. I'm saying that Github is going to apply the dark styles by default soon (without the modifier class) and the only way to revert the header will be to rewrite the old styles.