/**
 * Validates whether a font size value is safe to use in inline styles.
 * Accepts numeric values with valid CSS units, plain numbers, and CSS variables.
 *
 * @param size - The font size value to validate
 * @returns True if the font size is a valid format, false otherwise
 *
 * @example
 * isValidFontSize('14'); // true - plain number
 * isValidFontSize('14px'); // true - with px unit
 * isValidFontSize('1.5rem'); // true - with rem unit
 * isValidFontSize('var(--typography-base-sizes-small-font-size)'); // true - CSS variable
 * isValidFontSize('14px; background: red'); // false - CSS injection attempt
 */
export default function isValidFontSize(size: string): boolean;