/**
 * Find an opacity modifier slash without mistaking a slash inside a CSS color
 * function for the utility modifier.
 *
 * `bg-red-500/50` and `bg-[rgb(1_2_3)]/[0.5]` have a top-level modifier,
 * while `bg-[rgb(1_2_3_/_0.5)]` carries its alpha inside `rgb(...)`.
 */
export declare function colorModifierSlashIndex(value: string): number;