Common primary/background colours I use so I don't forget

theme.css

:root {
    --primary: #192734;
    --primary-alt: #384047;
    --background: #f2f2f2;
    --surface: #caccce;
}

:root[data-theme="dark"] {
    --primary: rgba(255, 255, 255, 0.85);
    --primary-alt: rgba(217, 217, 217, 0.85);
    --background: #242424;
    --surface: hsla(0, 0%, 40%, 0.48);
}

theme_brown.css

:root {
  --primary:#504621;
  --background:#e3decb;
  --surface:#afa275;
}

:root[data-theme=dark] {
  --primary:#d8d0b4;
  --background:#383427;
  --surface: #736b51;
}

theme_olive.css

:root {
  --primary: #464820;
  --background: #dddfca;
  --surface: #a2a573;
}

:root[data-theme=dark] {
  --primary: #cfd2b3;
  --background: #343527;
  --surface: #6b6d50;
}

theme_orange.css

:root {
  --primary: #5a4123;
  --background: #e9dbcc;
  --surface: #bc9c77;
}

:root[data-theme=dark] {
  --primary: #e1ccb5;
  --background: #3c3227;
  --surface: #7b6852;
}