#376FA6

CSS

:root {
  --muted-blue: #376fa6;
  --muted-blue-rgb: 55 111 166;
  --muted-blue-oklch: oklch(0.53 0.105 250.1);
}

.element {
  color: var(--muted-blue);
  background-color: hsl(210 50% 43%);
  border-color: oklch(0.53 0.105 250.1);
}

Tailwind CSS v4

@theme {
  --color-muted-blue: #376fa6;
  --color-muted-blue-50: #e0f8ff;
  --color-muted-blue-100: #cfebff;
  --color-muted-blue-200: #b4d8ff;
  --color-muted-blue-300: #90bbec;
  --color-muted-blue-400: #6da3da;
  --color-muted-blue-500: #4b8ac9;
  --color-muted-blue-600: #4075aa;
  --color-muted-blue-700: #335e88;
  --color-muted-blue-800: #224565;
  --color-muted-blue-900: #173047;
  --color-muted-blue-950: #071c2e;
}

SCSS

$muted-blue: #376fa6;
$muted-blue-rgb: 55, 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);
}