JS works in Codepen and JSfiddle but not in actual browswer

I made this super simple website to count down time since a certain date. I am not familiar with java script at all and copied the JavaScript and altered it to suite my needs.

As the title says it works in JSfiddle and Codepen but I can’t get it to work in my browser through Brackets.

Could someone take a look at the code and see if there are any glaring mistakes?

Here is the JSfiddle

Firstly, welcome to the forums.

While we are primarily here to help people with their Free Code Camp progress, we are open to people on other paths, too. Some of what you are asking is pretty trivial in the Free Code Camp context, so you might find that if you’re not getting the instruction and material you need in your current studies, the FCC curriculum will really help you get started. At a modest guess I’d say investing a 4-5 hours working through the curriculum here will really pay off. You can find the curriculum at http://freecodecamp.com.