CSS Functions Not Working

I'm new to using CSS. I am currently working my way through the "Front End Development" video training series, but I am having some trouble getting a CSS function (converting pixels to REMs) to work. Can anyone tell me what I am doing wrong? I also have a video if you need more clarity:

_function.scss file code:

@function px2em($size-in-px, $base-size:$default-font-size) {
@return ($size-in-px/$base-size) + em;
}
@function px2rem($size-in-px) {
@return ($size-in-px/$default-font-size) + rem;
}

Video Link:
https://drive.google.com/a/teamlocal.org/file/d/1GTqBKVss51GQ9c4RSwCykdO...

Thanks,

Jeff