showProgressBar() {

		this.progressBar.classList.add( 'visible' );

		clearTimeout( this.hideProgressBarTimeout );

		if( this.Reveal.getConfig().scrollProgress === 'auto' && !this.draggingProgressBar ) {

			this.hideProgressBarTimeout = setTimeout( () => {
				if( this.progressBar ) {
					this.progressBar.classList.remove( 'visible' );
				}
			}, HIDE_SCROLLBAR_TIMEOUT );

		}

	}
Show the progress bar and, if configured, automatically hide
it after a delay.