PNG images aren't HTML: HTML / CSS code isn't an image.
HTML is a set of instructions to a browser to render text and objects in a particular way to display a page to a user. It's generated on the server and sent in a text format to the client browser.
PNG is an compressed image format that can be used to render a bitmap.
HTML can display images (even PNG images) via the
tag: HTML img tag
] shows how to do it.
But you can't "convert png image to html code" any more than you can "convert apples to pig's ears"!