#5974AE

CSS

:root {
  --endless-river: #5974ae;
  --endless-river-rgb: 89 116 174;
  --endless-river-oklch: oklch(0.563 0.096 264.5);
}

.element {
  color: var(--endless-river);
  background-color: hsl(221 34% 52%);
  border-color: oklch(0.563 0.096 264.5);
}

Tailwind CSS v4

@theme {
  --color-endless-river: #5974ae;
  --color-endless-river-50: #e9f5ff;
  --color-endless-river-100: #d9e8ff;
  --color-endless-river-200: #c1d4fe;
  --color-endless-river-300: #a1b7e9;
  --color-endless-river-400: #829ed8;
  --color-endless-river-500: #6685c6;
  --color-endless-river-600: #5770a7;
  --color-endless-river-700: #455a86;
  --color-endless-river-800: #304264;
  --color-endless-river-900: #212e46;
  --color-endless-river-950: #101a2d;
}

SCSS

$endless-river: #5974ae;
$endless-river-rgb: 89, 116, 174;
$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);
}