If I enter a %age for size (so it's dynamic), the ineteface accepts the entry. However, the code is written to the HTML page as 90 not 90%. If I add the % manually (so it's 90%, not just 90), the lightbox does function correctly. However, I can't edit it. The % signs confuse the lightbox editor, so all settings are ignored.

Hello Rick,

Unfortunately the lightbox interface is not created in order to be used with percents. If you need a dynamic size you can just leave the fields empty.