Function getWithFallback

Computes the styles for elt (or defaults to document.body) using fallback as a set of default values.

// Fetch styles
const styles = getWithFallback({
 my_var: `red`
}, element);

// Access --my-var, or if it doesn't exist returns 'red'
styles.my_var;
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Hyphen case (eg 'my-var') is a common way of delimiting words in CSS variables, but can't be (elegantly) used in object properties. Instead, use '_' in the object key, which is replaced with '-'.

The leading '--' is not needed either.