I want to change the html, css, javascript of django admin panel because default admin panel is very ugly. Is it possible and if so, how can I do ?
For that I will suggest you to read this full documentation of Django for admin panel here is the link
In short form you have to visit this link https://docs.djangoproject.com/en/3.2/ref/contrib/admin/ and here yo will find all the admin related template download it and in your main projects template folder create a folder name admin and in that paste and do the changes as you want but be very careful while working in these template and for customizing model you have to change you admin.py acc to your need you will find all the detail how to do it in first mentioned link
I would recommend you to please read the full documentation and then start implementing it