[BUG] Tokens for font sizes are not being create as rem values.

[mariannuar]

Describe the bug When creating tokens, font sizes are being created as px values instead of rem values. However, the values is coming without the px word, only the value itself. So when using tokens for font sizes, the sizes of the fonts are not changing.

To Reproduce Steps to reproduce the behavior:

1. Run npm run develop
2. Go to http://localhost:6006/?path=/story/components-button--button
3. Open the inspector and inspect the font size of any Button text
4. Scroll down to the styles tab/section in the inspector
5. You can see that the button text is using the --font-size-body, and this value is coming as 18 instead of 18px or 1.125rem.

Expected behavior Font sizes tokens should be coming in this way 18px or the rem value, instead of only 18. It would be better if the value comes as they were coming before, in rem values.

Screenshots

[amazingrando]

This may relate to #102.