The Galaxy icon theme is no longer included in LibreOffice but is only available as extension. https://extensions.libreoffice.org/extensions/galaxy-icon-theme/1.0
Please contact the Design team, if you want to make an improvement to the Galaxy icon theme. Keep in mind, that the Galaxy icon theme uses 26x26 pixels icons, in contrast to all the other themes, which use 24x24 pixels icons. Besides that, there exists no SVG-source for the icons.
I suggest a WONTFIX for all the Galaxy related issues. The icon theme can still be improved, but outside this issue tracker.
Galaxy Theme was removed in LO 6.1