#3F6486

CSS

:root {
  --mississippi-river: #3f6486;
  --mississippi-river-rgb: 63 100 134;
  --mississippi-river-oklch: oklch(0.49 0.069 247.4);
}

.element {
  color: var(--mississippi-river);
  background-color: hsl(209 36% 39%);
  border-color: oklch(0.49 0.069 247.4);
}

Tailwind CSS v4

@theme {
  --color-mississippi-river: #3f6486;
  --color-mississippi-river-50: #e7f7ff;
  --color-mississippi-river-100: #d7eaff;
  --color-mississippi-river-200: #bed7f1;
  --color-mississippi-river-300: #9dbbda;
  --color-mississippi-river-400: #7ea3c6;
  --color-mississippi-river-500: #608bb2;
  --color-mississippi-river-600: #527596;
  --color-mississippi-river-700: #415e79;
  --color-mississippi-river-800: #2e4559;
  --color-mississippi-river-900: #1f303e;
  --color-mississippi-river-950: #0e1c27;
}

SCSS

$mississippi-river: #3f6486;
$mississippi-river-rgb: 63, 100, 134;
$mississippi-river-light: mix(#fff, $mississippi-river, 20%);
$mississippi-river-dark: mix(#000, $mississippi-river, 20%);

.element {
  color: $mississippi-river;
  box-shadow: 0 0 0 2px rgba($mississippi-river, 0.35);
}