wp-calypso/client/assets/stylesheets/shared/functions/_overflow-gradient.scss

// ==========================================================================
// Returns a linear gradient used to fade elements extending outside their parent
//
// The input value for the function must be individual RGB values. For conversion
// of hexadecimal color values please use the hex-to-rgb() color function.
//
// The rgba() notation needs to be escaped in order to support CSS custom
// properties. If it were not escaped SASS would interpret it as a SASS color
// function which doesn't allow for CSS custom properties as input values.
//
// Usage:
// background: overflow-gradient( var( --color-sidebar-background-rgb ) );
// border-image: overflow-gradient( var( --color-neutral-light-rgb ) ), to left );
// ==========================================================================
@function overflow-gradient( $color, $stop: 90%, $direction: to right ) {
	@return linear-gradient(
		$direction,
		transparent,
		$color $stop
	);
}