Thanks very much, Scott, Pmario, and Jeremy. The bookmark I grabbed was definitely line-based instead of outline-based, that was an issue.
I just downloaded Inkscape and drew myself a new icon, making sure it was outline-based.
I ran it through that SVGOMG page.
I’m still not seeing it darken on hover (actually it’s dark all the time).
This is my bookmark toolbar code:
<$action-sendmessage $message="tm-new-tiddler" title="New Bookmark" tags="Bookmarks [[Read Later]]"/>
<$button actions=<<new-bookmark-action>> tooltip="Add a new bookmark" aria-label="Add Bookmark" class=<<tv-config-toolbar-class>> >
<$text text="Add Bookmark"/>
And this is the SVG:
<svg xmlns="http://www.w3.org/2000/svg" width="210" height="297">
<path d="M181.103 4.734a66.257 2.753-19.797 2.621-44.094 [... big pile of numbers snipped for brevity... it's just one path, that's all it is.. ] 88-2.076-5.101-2.136a3.204 3.204 0 0 0-.353-.01z" />
I snipped the fill style out of it, and a stroke-width style.
I’m not sure what’s left to simplify…unless there’s something about that path that’s not cricket. (I could paste the whole path if that’s helpful)