Input:
@startuml
hide circle
hide members
class A
A o--> B
B --|> A
@enduml
SVG Output generated with PlantUML 1.2025.0:
<svg xmlns=...
<path codeLine="6" d="M18.4843,40.3559 C11.5043,56.6059 13.8798,78.9481 20.8598,95.1781 " fill="transparent" id="A-B" style="stroke:#181818;stroke-width:1;"/>
...
</svg>
Unexpected behaviour: Some elements have fill="transparent". This is a CSS named-color which is rendered transparend in browsers but not in pure SVG renderers such as Inkscape 1.4. Microsoft Word also shows black background depending of the context.

Expected behaviour: instead of fill="transparent" the SVG fill-opacity="0" should be used.
Possibly related to: https://forum.plantuml.net/12469/package-background-transparent-package-default-background
Links: