GitHub icons are not legible in dark mode

[AleksandrHovhannisyan]

Description

Steps to reproduce

1. Visit any page in dark mode.
2. Observe that the GitHub ::before images are not visible against the dark bg of the docs site.
3. Related issue: Observe that the text in the "add yours" sidebar wraps awkwardly due to the presence of the icon.

Solution

Not sure... We can do background-color: currentColor on that ::before, but then some of the background clips:

It also won't work for light mode.

Another idea was to use a background radial image, but it doesn't seem to be possible to layer that with a background-image without obscuring it, even if we make some parts of the color transparent.

Is there a way to get images without transparency from the API?