wp-calypso/client/assets/stylesheets/shared/mixins/_long-content-fade.scss

// ==========================================================================
// Long content fade mixin
//
// Creates a fading overlay to signify that the content is longer
// than the space allows.
//
// Note: To support CSS custom properties, any color that is passed in to
// the mixin needs to be escaped with the hex-to-rgb() function.
//
// Usage:
// @include long-content-fade();
// @include long-content-fade( $color: var( --color-sidebar-background ) );
// ==========================================================================

@mixin long-content-fade(
	$direction: right,
	$size: 20%,
	$color: var( --color-surface ),
	$edge: 0,
	$z-index: false
) {
	content: "";
	display: block;
	position: absolute;
	-webkit-touch-callout: none;
	-webkit-user-select: none;
	-khtml-user-select: none;
	-moz-user-select: none;
	-ms-user-select: none;
	user-select: none;
	pointer-events: none;

	@if $z-index {
		z-index: $z-index;
	}

	@if $direction == "bottom" {
		background: overflow-gradient($color, 90%, to top);
		left: $edge;
		right: $edge;
		top: $edge;
		bottom: calc(100% - $size);
		width: auto;
	}

	@if $direction == "top" {
		background: overflow-gradient($color, 90%, to bottom);
		top: calc(100% - $size);
		left: $edge;
		right: $edge;
		bottom: $edge;
		width: auto;
	}

	@if $direction == "left" {
		background: overflow-gradient($color, 90%, to left);
		top: $edge;
		left: $edge;
		bottom: $edge;
		right: auto;
		width: $size;
		height: auto;
	}

	@if $direction == "right" {
		background: overflow-gradient($color);
		top: $edge;
		bottom: $edge;
		right: $edge;
		left: auto;
		width: $size;
		height: auto;
	}
}