code: function decreasePageOffset(elements, currentOffset) {
      var canvas       = elements.canvas,
          tabOffsets   = getTabOffsets(elements),
          i, firstVisibleTabOffset;
  
      // Find the first fully visible tab in offset range
      for (i = 0; i < tabOffsets.length; i++) {
        if (tabOffsets[i] >= currentOffset) {
          firstVisibleTabOffset = tabOffsets[i];
          break;
        }
      }
  
      // Return (the first visible tab offset - the tabs container width) without going negative
      return Math.max(0, firstVisibleTabOffset - canvas.clientWidth);
    }
docs: Returns the offset for the next decreasing page.
  
  @param elements
  @param currentOffset
  @returns {number}