Add createThemeCss option to put CSS into a layer

[Phygon]

I suggest an option for createThemeCss() to put the CSS between @layer ${layer} { ... }, so that custom style overrides and Tailwind classes work without !important or other tricks. This is easy to do in the user code (see below), however not everybody is an expert in the arcane workings of CSS.

export function CodeBlockStyles() {
    return (
        <style>{`
            @layer components {
                ${themeCss}
            }
        `}</style>
    );
}

It could just look like this:

const themeCss = createThemeCss({
    light: solarizedLightTheme,
    dark: solarizedDarkTheme,
    darkSelector: '.dark',
    layer: 'components' // <- new
})

As an alternative, this 'trick' or any alternatives could be documented with an example.