Hi Ritika,
If you’re using a custom login page, then you can create a new page layout and apply that to only the login page.
Please see documentation : https://docs.mendix.com/refguide/layout
otherwise if you can use standard login page and you can provide the styling using custom .css file to change the theme.
Also you can change the elements such as div, span or input by using web modeller.
Please mark answer accepted if you find it helpful. Thank you.