#54779F

CSS

:root {
  --montreux-blue: #54779f;
  --montreux-blue-rgb: 84 119 159;
  --montreux-blue-oklch: oklch(0.559 0.074 252.4);
}

.element {
  color: var(--montreux-blue);
  background-color: hsl(212 31% 48%);
  border-color: oklch(0.559 0.074 252.4);
}

Tailwind CSS v4

@theme {
  --color-montreux-blue: #54779f;
  --color-montreux-blue-50: #e7f7ff;
  --color-montreux-blue-100: #d8eaff;
  --color-montreux-blue-200: #bfd7f4;
  --color-montreux-blue-300: #9ebadd;
  --color-montreux-blue-400: #7fa2ca;
  --color-montreux-blue-500: #6289b6;
  --color-montreux-blue-600: #53749a;
  --color-montreux-blue-700: #425d7c;
  --color-montreux-blue-800: #2e445b;
  --color-montreux-blue-900: #1f2f40;
  --color-montreux-blue-950: #0f1c29;
}

SCSS

$montreux-blue: #54779f;
$montreux-blue-rgb: 84, 119, 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);
}