Hi Ciaran
In my sites, I extensively use the CSS class 'caption' with template SKYLAR. Here is an example screenshot from the J3 version (s. SKYLAR_J3_Caption_ok.jpg). The image caption is displayed as expected.
In J4, the caption is not displayed (s. SKYLAR_J4_Caption_missing.jpg).
The HTML code of the article is identical for J3 and J4 and is shown in HTML_Code_of_Article.pdf.
The custom CSS is more or less identical for J3 and J4; all entries for all kinds of captions are identical. See my J4 custom.css in custom.css.pdf.
I also would like to bring to your attention that the display of the figure-element is not identical in the J3 and J4 versions of SKYLAR. In J3, the figcaption is inside the border of the figure-element (s. SKYLAR_J3_figcaption.jpg), whereas in J4 it is outside (s. SKYLAR_J4_figcaption.jpg).
Regards
Rolf