#5A76AC

CSS

:root {
  --endless-river: #5a76ac;
  --endless-river-rgb: 90 118 172;
  --endless-river-oklch: oklch(0.567 0.09 262.9);
}

.element {
  color: var(--endless-river);
  background-color: hsl(220 33% 51%);
  border-color: oklch(0.567 0.09 262.9);
}

Tailwind CSS v4

@theme {
  --color-endless-river: #5a76ac;
  --color-endless-river-50: #e9f5ff;
  --color-endless-river-100: #d9e8ff;
  --color-endless-river-200: #c1d4fc;
  --color-endless-river-300: #a1b7e7;
  --color-endless-river-400: #829ed4;
  --color-endless-river-500: #6685c2;
  --color-endless-river-600: #5771a4;
  --color-endless-river-700: #455a84;
  --color-endless-river-800: #304262;
  --color-endless-river-900: #212e45;
  --color-endless-river-950: #101a2c;
}

SCSS

$endless-river: #5a76ac;
$endless-river-rgb: 90, 118, 172;
$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);
}