#345D88

CSS

:root {
  --mississippi-river: #345d88;
  --mississippi-river-rgb: 52 93 136;
  --mississippi-river-oklch: oklch(0.469 0.084 251.1);
}

.element {
  color: var(--mississippi-river);
  background-color: hsl(211 45% 37%);
  border-color: oklch(0.469 0.084 251.1);
}

Tailwind CSS v4

@theme {
  --color-mississippi-river: #345d88;
  --color-mississippi-river-50: #e5f7ff;
  --color-mississippi-river-100: #d5eaff;
  --color-mississippi-river-200: #bcd7f8;
  --color-mississippi-river-300: #99bbe2;
  --color-mississippi-river-400: #79a2cf;
  --color-mississippi-river-500: #5b8abc;
  --color-mississippi-river-600: #4d759f;
  --color-mississippi-river-700: #3d5d80;
  --color-mississippi-river-800: #2b455e;
  --color-mississippi-river-900: #1d2f42;
  --color-mississippi-river-950: #0d1c2a;
}

SCSS

$mississippi-river: #345d88;
$mississippi-river-rgb: 52, 93, 136;
$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);
}