The bit you are looking for which is affecting the image size is the background-size: cover
If you need the whole image seen you will need to make that background-size: contain
So in the customCSS setting of the theme try adding
body#page-login-index {background-size: contain;}
https://www.w3schools.com/cssref/css3_pr_background-size.asp
If you need the whole image seen you will need to make that background-size: contain
So in the customCSS setting of the theme try adding
body#page-login-index {background-size: contain;}
https://www.w3schools.com/cssref/css3_pr_background-size.asp