#3A6CB8

CSS

:root {
  --matt-blue: #3a6cb8;
  --matt-blue-rgb: 58 108 184;
  --matt-blue-oklch: oklch(0.535 0.131 258.6);
}

.element {
  color: var(--matt-blue);
  background-color: hsl(216 52% 47%);
  border-color: oklch(0.535 0.131 258.6);
}

Tailwind CSS v4

@theme {
  --color-matt-blue: #3a6cb8;
  --color-matt-blue-50: #e0f7ff;
  --color-matt-blue-100: #cfe9ff;
  --color-matt-blue-200: #b4d6ff;
  --color-matt-blue-300: #91b8fb;
  --color-matt-blue-400: #6d9feb;
  --color-matt-blue-500: #4c85dc;
  --color-matt-blue-600: #4171b9;
  --color-matt-blue-700: #345a95;
  --color-matt-blue-800: #22436f;
  --color-matt-blue-900: #162e4e;
  --color-matt-blue-950: #081a34;
}

SCSS

$matt-blue: #3a6cb8;
$matt-blue-rgb: 58, 108, 184;
$matt-blue-light: mix(#fff, $matt-blue, 20%);
$matt-blue-dark: mix(#000, $matt-blue, 20%);

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