(styles): add support to provide external styles (as complete file content)

src/file/file.ts

@@ -25,6 +25,8 @@ export class File {
     private readonly footerWrapper: FooterWrapper;
     private readonly contentTypes: ContentTypes;
     private readonly appProperties: AppProperties;
+    private externalStyles: string;    
+    
 
     constructor(options?: IPropertiesOptions, sectionPropertiesOptions?: SectionPropertiesOptions) {
         this.document = new Document(sectionPropertiesOptions);
@@ -111,6 +113,10 @@ export class File {
         this.document.createDrawing(mediaData);
     }
 
+    public setExternalStyles(styles: string): void {
+        this.externalStyles = styles;
+    }
+
     public get Document(): Document {
         return this.document;
     }
@@ -154,4 +160,7 @@ export class File {
     public get AppProperties(): AppProperties {
         return this.appProperties;
     }
+    public get ExternalStyles(): string {
+        return this.externalStyles;
+    }
 }