Sadly, the teaser website isn't online anymore. If only someone kept an archive of the internet. This is where the Wayback Machine on [archive.org](https://archive.org/) comes in handy.
When taking a look at the source we find the following comment:
So, let's use the Wayback Machine to get the teaser page. <https://web.archive.org/web/20201112020839/https://adventofctf.com/>
When we take a look at the source html of the page we find the following comment:
```html
<!-- Ceasar worked on this you know. Tk9WSXtIRVlfMVNfVGgxU19AX0ZsYTk/fQ== -->
```
If we then use `base64` to decode this string we get `NOVI{HEY_1S_Th1S_@_Fla9?}`.
It looks like some encoded string. If you've been doing CTFs for a while you'll probably recognize it's encoded in `base64`. We can use the program `base64` to decode this string.