#396FA6

CSS

:root {
  --muted-blue: #396fa6;
  --muted-blue-rgb: 57 111 166;
  --muted-blue-oklch: oklch(0.53 0.104 250.8);
}

.element {
  color: var(--muted-blue);
  background-color: hsl(210 49% 44%);
  border-color: oklch(0.53 0.104 250.8);
}

Tailwind CSS v4

@theme {
  --color-muted-blue: #396fa6;
  --color-muted-blue-50: #e1f8ff;
  --color-muted-blue-100: #d0ebff;
  --color-muted-blue-200: #b5d8ff;
  --color-muted-blue-300: #91bbec;
  --color-muted-blue-400: #6ea3da;
  --color-muted-blue-500: #4d8ac9;
  --color-muted-blue-600: #4275a9;
  --color-muted-blue-700: #345d88;
  --color-muted-blue-800: #234565;
  --color-muted-blue-900: #173047;
  --color-muted-blue-950: #081c2e;
}

SCSS

$muted-blue: #396fa6;
$muted-blue-rgb: 57, 111, 166;
$muted-blue-light: mix(#fff, $muted-blue, 20%);
$muted-blue-dark: mix(#000, $muted-blue, 20%);

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