I noticed from login.php that some steps seem to have been taken to convert OpenEMR to bootstrap.
There is bootstrap styling present in login.php (v5.0.0), but I noticed that the page isn’t rendering properly on a mobile device:
If you add the following line following <meta http-equiv="X-UA-Compatible" content="IE=edge" />
after the opening <head>
tag I think you will see an improvement:
<meta name="viewport" content="width=device-width, initial-scale=1">
The same can probably done on some other pages with bootstrap, thought it probably won’t help that much if the page contains iframes.