WEBSITE-416 implements its solution for boxshadow borders on images by requiring the author to specify [.boxshadow] above an image reference. E.g.
for inline image references or
for a block image reference.
This is based on the presence of the following CSS in content/css/jenkins.css file:
It would be better if implement this on a page-specific basis using Asciidoctor's docinfo features, which would provide the ability to implement CSS customizations on a page specific basis.