docs: function _reLayout (context, virtualRect, ltbr) {
    const el = context.$el
    const rect = _getIndicatorRect(el)
    const rectWithPx = Object.keys(rect).reduce((pre, key) => {
      pre[key] = rect[key] + 'px'
      return pre
    }, {})
    extend(el.style, rectWithPx)
    const axisMap = [
      { dir: ltbr.left ? 'left' : ltbr.right ? 'right' : 'left', scale: 'width' },
      { dir: ltbr.top ? 'top' : ltbr.bottom ? 'bottom' : 'top', scale: 'height' }
    ]
    Object.keys(axisMap).forEach(key => {
      const { dir, scale } = axisMap[key]
      el.style[dir] = ltbr[dir] + virtualRect[scale] / 2 - rect[scale] / 2 + 'px'
    })
  }