SCSS - Black with Opacity

black opacity.css

/// Generates the color black, with, optionally, a set opacity.
/// @access public
/// @param {Float} $opacity - Opacity
/// @example scss - Usage
///   .foo {
///     border-color: black(0.1);
///   }
/// @example css - Result
///   .foo {
///     border-color: rgba(0, 0, 0, 0.1);
///   }
@function black($opacity) {
    @return rgba(0, 0, 0, $opacity);
}