As I’d decided with mauricio that I will apply bootstrap classes on the individual elements across different pages once I finish with the basic layout(grid structure), I’ve started working on that line.
I have applied form classes to the login page. The following PR addresses the same.
https://github.com/phpmyadmin/phpmyadmin/pull/15364
Bootstrap card classes have also been added to home page.
https://github.com/phpmyadmin/phpmyadmin/pull/15369
GSoC PMA 