Set a gradient as the background, then color: transparent plus background-clip: text so the gradient is visible only through the glyph outlines. The -webkit- prefix is still needed in some browsers.
Enlarging background-size and animating background-position makes the gradient appear to flow — a shine effect layered on top of the fill.
When to use
Use for brand wordmarks and hero headlines. Avoid it in body copy, and don’t let text meaning depend on colour alone for colour-blind users.