function resetVerticalSlides() {

		getHorizontalSlides().forEach( horizontalSlide => {

			Util.queryAll( horizontalSlide, 'section' ).forEach( ( verticalSlide, y ) => {

				if( y > 0 ) {
					verticalSlide.classList.remove( 'present' );
					verticalSlide.classList.remove( 'past' );
					verticalSlide.classList.add( 'future' );
					verticalSlide.setAttribute( 'aria-hidden', 'true' );
				}

			} );

		} );

	}
Resets all vertical slides so that only the first
is visible.