wp-calypso/packages/components/src/styles/_clear-fix.scss

// ==========================================================================
// Clear fix mixin (clearfix)
// ==========================================================================

@mixin a8c-clear-fix {
	&::after {
		content: ".";
		display: block;
		height: 0;
		width: 0;
		clear: both;
		visibility: hidden;
		overflow: hidden;
	}
}