Modal close icon is not visible

[NikLP]

Per title - an example is, set a webform to open in a modal, the X icon is visible in the source code but is not apparent in the front-end.

The same icon is visible if switching to Gin theme (for example).
Discovered via a subtheme, but on inspection same scenario apparent in localgov_base.

Modal in Gin

Modal in Base theme

Source code sample indicating presence of Close elements