So for enterprise development you need a ponyfill to support this.
Otherwise, you could certainly set up your theme.css to have a set of CSS Variables you reuse in the rest of your CSS files, then dynamically change between light-theme or dark-theme or other custom themes with JS
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So, why would you prefer this to CSS variables?
Can you elaborate more?
CSS Variables for one aren't supported in IE11 : caniuse.com/#feat=css-variables
So for enterprise development you need a ponyfill to support this.
Otherwise, you could certainly set up your theme.css to have a set of CSS Variables you reuse in the rest of your CSS files, then dynamically change between light-theme or dark-theme or other custom themes with JS