Just get the post of This Page does not use JS" by Joel. It shows the ability of use
<style> tag in the
"We forget that it’s just another HTML element." - By Joel
This can be a method to display the UI guideline as this method allows to display the expected style as the source CSS code displaying inside.
Below is a demo that I played with the style tag on codepen.io. By adding the attribute "contenteditable" , you can edit the style and preview the outcome immediately on the page.
See the Pen Style Tag for CSS Style Demo by Millie (@witmin) on CodePen.