/**
 * Normalizes a CSS dimension value.
 *
 * - Negative values are rejected.
 * - Explicit CSS units (`px`, `rem`, `em`, `%`) are preserved.
 * - Unitless numeric values are converted to pixels.
 *
 * @param value - The CSS value to normalize (e.g., "16px", "1rem", "100%")
 * @returns A normalized CSS value, or `undefined` if the value is absent, negative, or cannot be parsed
 */
export declare function normalizeCssDimension(value: string | undefined): string | undefined;