createSlideBlock_(elem) {
    // Wraps the slide around a container
    const wrap = DOM.wrap(elem.el, 'div');
    wrap.className = CLASSES.WRAP;
    wrap.setAttribute('id', `zoomed-${elem.el.getAttribute('id')}`);

    // Slide container, need due to flexbox styles
    const div = DOM.wrap(wrap, 'div');
    div.className = CLASSES.DIV;

    // Adding some layer for controlling click events
    const divLayer = DOM.createNode('div');
    divLayer.className = 'zoom-layer';
    divLayer.addEventListener('click', e => {
      e.stopPropagation();
      this.zoomOut();
      this.ws_.goToSlide(elem.i);
    });
    wrap.appendChild(divLayer);

    // Slide number
    const slideNumber = DOM.createNode('p', '', `${elem.i + 1}`);
    slideNumber.className = 'text-slide-number';
    div.appendChild(slideNumber);
  }
Creates a block structure around the slide.
@param {Element} elem slide element.