#5A769E

CSS

:root {
  --montreux-blue: #5a769e;
  --montreux-blue-rgb: 90 118 158;
  --montreux-blue-oklch: oklch(0.56 0.071 257.3);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(215 27% 49%);
  border-color: oklch(0.56 0.071 257.3);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5a769e;
  --color-montreux-blue-50: #e9f6ff;
  --color-montreux-blue-100: #dae9ff;
  --color-montreux-blue-200: #c3d6f3;
  --color-montreux-blue-300: #a2b9dc;
  --color-montreux-blue-400: #84a0c8;
  --color-montreux-blue-500: #6888b5;
  --color-montreux-blue-600: #587399;
  --color-montreux-blue-700: #475c7b;
  --color-montreux-blue-800: #32445b;
  --color-montreux-blue-900: #222f3f;
  --color-montreux-blue-950: #111b28;
}

SCSS

$montreux-blue: #5a769e;
$montreux-blue-rgb: 90, 118, 158;
$montreux-blue-light: mix(#fff, $montreux-blue, 20%);
$montreux-blue-dark: mix(#000, $montreux-blue, 20%);

.element {
  color: $montreux-blue;
  box-shadow: 0 0 0 2px rgba($montreux-blue, 0.35);
}