UI/Spinner graphic placement bug

[blankenberg]

Describe the bug
UI quirk:
In admin panel --> users --> filter box --> enter string --> hit enter --> "center panel goes gray and nothing happens"

What actually happens is that the spinner graphic is placed halfway down the total (scrollable) page, instead of halfway down the visible screen.

Galaxy Version and/or server at which you observed the bug
usegalaxy.org:
Galaxy version 25.1.rc1, commit a3c19d87111d4f28f258479496681d9def9b6b97

Browser and Operating System
Operating System: Linux,
Browser: Chrome

To Reproduce
Steps to reproduce the behavior:

1. Go to description

Expected behavior
spinner should be visible on the screen

Screenshots
If applicable, add screenshots to help explain your problem.

Additional context
If shared framework, may occur elsewhere also.