It looks like the issue is that the string class for the light theme is:
.highlight .s {
color: #dd2200;
background-color: #fff0f0;
}
But for the dark theme it's:
@media (prefers-color-scheme: dark)
.highlight .s {
color: #e6db74;
}
And so it winds up using the dark color, but with the light
background, because the dark theme doesn't specify a background.
