title: How can I do a countdown timer with html?
body: <p>I'm helping my I.T teacher to create easter eggs for some tasks, and I would like to create a countdown timer with html.
  Explanation:
  Everytime you enter into a website, the countdown timer starts.
  Example:
  I have a html code with a countdown timer at 30 min, if I go into the website, the countdown timer starts going down, but if I refresh the website, it reset.
  I hope you will understand, thanks!</p>