OPAC Pop-up Improvements

[Terran McCanna]

Suggested changes based on feedback from a usability study done by Mercer University:

Most pop-ups tend to appear on the top third of the browser window rather than the center, and are not strongly distinguished from the background. This makes it difficult for people who wear bifocals to 1) notice and 2) read. This is a bigger problem on Chrome than on Firefox, but could be improved on both.

This could be resolved by using custom-styled pop-ups rather than the browser's default style. The custom pop-ups could be centered in the page, visually distinguished from the parent window, and have a larger font size.

[Terran McCanna (tmccanna)]

See attached screenshot showing how pop-up is not well-differentiated from background.