#5B769D

CSS

:root {
  --montreux-blue: #5b769d;
  --montreux-blue-rgb: 91 118 157;
  --montreux-blue-oklch: oklch(0.561 0.069 257.5);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(215 27% 49%);
  border-color: oklch(0.561 0.069 257.5);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5b769d;
  --color-montreux-blue-50: #eaf6ff;
  --color-montreux-blue-100: #dbe9ff;
  --color-montreux-blue-200: #c3d5f2;
  --color-montreux-blue-300: #a3b9db;
  --color-montreux-blue-400: #85a0c7;
  --color-montreux-blue-500: #6988b4;
  --color-montreux-blue-600: #597398;
  --color-montreux-blue-700: #475c7a;
  --color-montreux-blue-800: #32435a;
  --color-montreux-blue-900: #222f3f;
  --color-montreux-blue-950: #111b28;
}

SCSS

$montreux-blue: #5b769d;
$montreux-blue-rgb: 91, 118, 157;
$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);
}