#5B769F

CSS

:root {
  --montreux-blue: #5b769f;
  --montreux-blue-rgb: 91 118 159;
  --montreux-blue-oklch: oklch(0.561 0.071 258.6);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(216 27% 49%);
  border-color: oklch(0.561 0.071 258.6);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5b769f;
  --color-montreux-blue-50: #eaf6ff;
  --color-montreux-blue-100: #dbe9ff;
  --color-montreux-blue-200: #c3d5f4;
  --color-montreux-blue-300: #a3b8dd;
  --color-montreux-blue-400: #85a0c9;
  --color-montreux-blue-500: #6987b6;
  --color-montreux-blue-600: #597399;
  --color-montreux-blue-700: #475c7b;
  --color-montreux-blue-800: #32435b;
  --color-montreux-blue-900: #222f40;
  --color-montreux-blue-950: #111b29;
}

SCSS

$montreux-blue: #5b769f;
$montreux-blue-rgb: 91, 118, 159;
$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);
}