extjs/templates/admin-dashboard/classic/sass/src/view/authentication/LockingWindow.scss

   1 .auth-locked-window{
   2     .x-window-body {
   3         background-image:url('images/lock-screen-background.jpg');
   4         background-size:cover;
   5         background-repeat:repeat;
   6     }
   7
   8     &.x-window-default {
   9         border: none;
  10         border-radius: 0;
  11         padding: 0;
  12     }
  13 }