HTML files (HTML in your android phone folders in File Manager) You can make a new file and add your HTML file there and so the picture you will need:
+CREATE FOLDER (HTML FILES)
+ADD FILES(Needed.png, Webdesign.html)
You just need to do like src="Needed.png"
You do not need to add a separate file for .js and css because you can directly inject them into HTML
CSS: <style> </style>