Theme-Aware Favicons
Drag the slider through the three browser themes. With the effect off, all three favicons stay solid black, and on a dark or black tab strip they simply vanish. Turn it on and the same marks invert to stay legible.
The switch cannot come from your stylesheet, because a favicon is a separate file and your CSS has no reach into browser chrome. The media query has to live inside the SVG, which is why so many sites ship a black square and never notice.