Background information

CSS custom properties will simplify CSS rules for theming and help with the long term maintainability of the CSS. More info:

https://developer.mozilla.org/en-US/docs/Web/CSS/Using_CSS_custom_properties
https://caniuse.com/#search=css%20custom

What

• Define CSS custom properties for semantic colors - for example "paper background", "primary text", "secondary text" etc
• Utilize those custom properties for theme-able rules instead of separate rules for each theme class