Border on WP Gallery image enlargements

[Anna]

Anna

May 30, 2016 at 3:04 pm

I’m using the WordPress Gallery system to display images, the enlargements appear on the overlay. Click on any thumb here:
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We need to add a thin white border to the enlargement, but I can’t figure out how to tweak the CSS to make that happen.
I added the below CSS to the Custom CSS Box in the Advanced area of the Theme Settings, and this IS putting a border on – but it’s around the whole ‘box’, including the caption area below the image and the area above the image. We need the border added to the actual image only.

.mfp-img {
border: 1px solid #fff;
}

I’m using a child theme of Virtue which includes some other small tweaks, as well as commented-out CSS in my attemps to tweak a border.
Is there a way to do this?
Any help appreciated, thanks,
Annette