Have It All: External, Styleable, & Scalable SVG | Scott Jehl, Web Designer/Developer
Briefly

The SVG use element offers a means of referencing SVG symbols, whether in the same page or external files, allowing for scalable and styleable SVGs. External SVGs can use global CSS custom properties defined on the page for styling.
In order for CSS color variables to work in SVG, the file must leverage the same CSS custom properties for fills and strokes. This method demands using the preferred CSS custom property first, followed by the fallback color.
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