#5B769E

CSS

:root {
  --montreux-blue: #5b769e;
  --montreux-blue-rgb: 91 118 158;
  --montreux-blue-oklch: oklch(0.561 0.07 258.1);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(216 27% 49%);
  border-color: oklch(0.561 0.07 258.1);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5b769e;
  --color-montreux-blue-50: #eaf6ff;
  --color-montreux-blue-100: #dbe9ff;
  --color-montreux-blue-200: #c3d5f3;
  --color-montreux-blue-300: #a3b9dc;
  --color-montreux-blue-400: #85a0c8;
  --color-montreux-blue-500: #6988b5;
  --color-montreux-blue-600: #597399;
  --color-montreux-blue-700: #475c7a;
  --color-montreux-blue-800: #32435b;
  --color-montreux-blue-900: #222f3f;
  --color-montreux-blue-950: #111b28;
}

SCSS

$montreux-blue: #5b769e;
$montreux-blue-rgb: 91, 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);
}