Ps: if you want to reset the site, just press “F5” to refresh the site, and the Header will be there again for you.
When you press the button to "hide" the header, you are calling this style (css file), which simply "hides" from your web browser all the header section that Quora shows each time we are reading content.
If you find an error, or want to help, or know more about this idea, you can go to the Hide-Quora Github repository.