Customizing the Lightbox when it goes full screen?

Is there a way to customize or alter the lightbox settings when it is opened up to full screen. My image captions are being cut off and it would be nice to change how the captions look as well. Is there a way to do this without building a custom modal from scratch or are these settings locked away?

Here is my site Read-Only: LINK
(how to share your site Read-Only link)

If you inspect the Lightbox in developer tools you can see the CSS rules that affect it. You can then write custom CSS to override values.