Unfortunately the icons using the style tag element. I strongly suggest to use an inline style notation, either as SVG attribute or inline CSS (it is also a baseless to use globale CSS for a single SVG element). Examples:
- https://commons.wikimedia.org/wiki/File:VisualEditor_-_Icon_-_Article-ltr_dimmed.svg
- https://commons.wikimedia.org/wiki/File:VisualEditor_-_Icon_-_Link-ltr-invert.svg
T68672 - libRSVG bug (strangely first in 2014)
Additional there are some more (global) style-tag bugs for the libRSVG e.g. https://commons.wikimedia.org/wiki/Help:SVG#Font_styling_class