This is happening partly because those symbols are actually images, specifically .svg vectors.
There is a related issue where .svg figures are rendered correctly, but are illegible when using the dark theme because the .svg has black text on a transparent background. This is fine when using the light theme, which uses a white background, but the transparent layer becomes black when using the dark theme and thus renders black text on a black background that is illegible.
This is happening partly because those symbols are actually images, specifically .svg vectors.
There is a related issue where .svg figures are rendered correctly, but are illegible when using the dark theme because the .svg has black text on a transparent background. This is fine when using the light theme, which uses a white background, but the transparent layer becomes black when using the dark theme and thus renders black text on a black background that is illegible.