I want to change file icons of some specific file types like- .html, .css etc.
I have tried using "File Type Editor (assogiate)" which is not working. I have also tried using "Gnome Tweak Tool" using icon themes. But that also does not worked properly (Though I can change folder icons , dash menu icons but not file icons).

Please suggest me a way so that I can change file icons properly. I have read some of the articles saying about some mime type changes. I could not get proper guide from any of those articles. If there is such a way then please write in detail.

Many Many Thanks in Advance :)