#5575B8

CSS

:root {
  --endless-river: #5575b8;
  --endless-river-rgb: 85 117 184;
  --endless-river-oklch: oklch(0.568 0.111 263.9);
}

.element {
  color: var(--endless-river);
  background-color: hsl(221 41% 53%);
  border-color: oklch(0.568 0.111 263.9);
}

Tailwind CSS v4

@theme {
  --color-endless-river: #5575b8;
  --color-endless-river-50: #e6f5ff;
  --color-endless-river-100: #d7e8ff;
  --color-endless-river-200: #bed4ff;
  --color-endless-river-300: #9db7f1;
  --color-endless-river-400: #7d9ee0;
  --color-endless-river-500: #6084cf;
  --color-endless-river-600: #5270af;
  --color-endless-river-700: #41598c;
  --color-endless-river-800: #2d4269;
  --color-endless-river-900: #1e2d49;
  --color-endless-river-950: #0e1a30;
}

SCSS

$endless-river: #5575b8;
$endless-river-rgb: 85, 117, 184;
$endless-river-light: mix(#fff, $endless-river, 20%);
$endless-river-dark: mix(#000, $endless-river, 20%);

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