refactor: Use empty object as customStyles' default value to reflect the accepted data type

Author: oluwatobiss

src/ImageGallery.tsx

@@ -8,7 +8,7 @@ export function ImageGallery({
   columnWidth = 230,
   gapSize = 24,
   fixedCaption = false,
-  customStyles = undefined,
+  customStyles = {},
 }: ImageGalleryPropsType) {
   const [imageSrc, setImageSrc] = useState<string | undefined>(undefined);
   const [slideNumber, setSlideNumber] = useState(1);

src/ImageGalleryStyles.ts

@@ -5,7 +5,7 @@ export function imageGalleryStyles(
   columnWidth?: string | number,
   gapSize?: number,
   fixedCaption?: boolean
-) : ImageGalleryStylesType {
+): ImageGalleryStylesType {
   const galleryContainerStyle: React.CSSProperties = {
     columnCount,
     columnWidth: `${columnWidth}px`,