(Samuel said)
That should be in /boot. Do you have /boot on a separate partition?
How do I determine which partition /boot is in?
The directory mentioned in the error messages is under /boot as you said
(thank-you!):
---------------
-bash.2[system]: pwd
/boot/grub2/themes/system
-bash.3[system]: ls -la
total 7080
drwxr-xr-x. 2 root root 1024 Oct 11 12:59 .
drwxr-xr-x. 4 root root 1024 May 9 2012 ..
-rw-r--r--. 1 root root 3621581 May 23 2017 background.png
-rw-r--r--. 1 root root 3621581 May 23 2017 fireworks.png
-bash.4[system]:
---------------
Are there log files somewhere that have the full error messages showing
specifically what 4 things are wanted but missing?