Comment 1 for bug 1839369

I added a new 'sronly' class that moves an element off the screen so that it won't be visible to sighted users, but will be readable in the appropriate location for screen readers. This approach is recommended by: https://webaim.org/techniques/css/invisiblecontent/

My patch for review is here:

https://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/user/mccanna/lp1839369_placeholder_accessibility