Creating a new modal in Backlight 3 is easy, and can be done without diving into Custom Stylesheets or PHPlugins. That’s because Backlight 3 already rocks jQuery and Fancybox on every page (assuming a Pangolin-based template), and so you needn’t add any new dependencies.
To modal, you need just two things: a trigger, and content.
Anywhere in Backlight that accepts HTML, mark it up like this, ensuring the trigger’s
href references the contents’
<a href="#myModal" data-fancybox> Trigger </a> <div id="myModal" style="display: none;"> <p>Content</p> </div>
… and have a nice day.