Tabs in the settings window are unreadable in light theme

[eritbh]

Related to #92

A quick CSS fix, tested in the inspector, though this does also make the inactive tab text a bit dimmer in dark mode:

header > div {
  color: var(--text-muted);
}
header > div.active {
  color: inherit;
}

It doesn't look like the content of this window is actually in this repo, since it's pulled in from an external page I couldn't track down a repo for, so I can't submit a PR to fix this - hopefully this is something that can be patched easily on your end.