BetterSEQTA-Plus/src/inject/injected/theme.css

html.dark {
  --background-primary: #232323;
  --background-secondary: #1a1a1a;
  --text-primary: white;
}

html:not(.dark) {
  --background-primary: #ffffff;
  --background-secondary: #e5e7eb;
  --text-primary: black;
}