Hi. I used the solution from this thread for a simple full-screen image modal routine. I use it for images associated with my tiddlers via URLs in an image field.
<$button message="tm-modal" param="ModalImage" set="$:/state/currentImage" setTo=
{{!!illustration}} class='tc-btn-invisible'>
<$image class='titlethumb' source={{!!illustration}} />
</$button>
Here’s the tiddler ModalImage.json (240 Bytes) that shows the “dynamic” image, and the related CSS (1.5 KB).
The CSS is namespaced to a “fullsize” class which is added to the modal via a class field on the dynamic image tiddler.