function shuffle( slides = getHorizontalSlides() ) {

		slides.forEach( ( slide, i ) => {

			// Insert the slide next to a randomly picked sibling slide
			// slide. This may cause the slide to insert before itself,
			// but that's not an issue.
			let beforeSlide = slides[ Math.floor( Math.random() * slides.length ) ];
			if( beforeSlide.parentNode === slide.parentNode ) {
				slide.parentNode.insertBefore( slide, beforeSlide );
			}

			// Randomize the order of vertical slides (if there are any)
			let verticalSlides = slide.querySelectorAll( 'section' );
			if( verticalSlides.length ) {
				shuffle( verticalSlides );
			}

		} );

	}
Randomly shuffles all slides in the deck.