Want to open wp-admin on my domain name if any one enter

Can any one let me know how should i do this, i read many article regarding the same but didn’t succeed, my issue is if anyone hit my domain name such as https://blog.manishagarwal.com it should open the wordpress default login page (wp-admin).
i tried to edit in wp-config.php:

when i use above code the stylesheet of home page is not working and also it not redirect to.

please do suggest me how to get this done.