Focus rings with nested contrast-color()?

An exploration of using nested `contrast-color()` CSS functions to automatically generate accessible focus ring styles from a single background color token. The technique uses `contrast-color(contrast-color(var(--page-bg)))` to derive both the outer ring and inner highlight colors. The post also weighs this against using `color-scheme` with `light-dark()` as a simpler, better-supported alternative for theming focus rings across light and dark modes, ultimately recommending the latter for its readability and broader browser support.