#5B75A1

CSS

:root {
  --montreux-blue: #5b75a1;
  --montreux-blue-rgb: 91 117 161;
  --montreux-blue-oklch: oklch(0.56 0.075 260.7);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(218 28% 49%);
  border-color: oklch(0.56 0.075 260.7);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #5b75a1;
  --color-montreux-blue-50: #eaf6ff;
  --color-montreux-blue-100: #dbe9ff;
  --color-montreux-blue-200: #c3d5f5;
  --color-montreux-blue-300: #a3b8df;
  --color-montreux-blue-400: #859fcb;
  --color-montreux-blue-500: #6987b8;
  --color-montreux-blue-600: #59729c;
  --color-montreux-blue-700: #475b7d;
  --color-montreux-blue-800: #32435c;
  --color-montreux-blue-900: #222e41;
  --color-montreux-blue-950: #111b29;
}

SCSS

$montreux-blue: #5b75a1;
$montreux-blue-rgb: 91, 117, 161;
$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);
}