code: def _create_tooltips(hist: Histogram1D, vega: dict, kwargs: dict):
      
      if kwargs.pop("tooltips", False):
          vega["signals"] = vega.get("signals", [])
          vega["signals"].append({
            "name": "tooltip",
            "value": {},
            "on": [
              {"events": "rect:mouseover", "update": "datum"},
              {"events": "rect:mouseout",  "update": "{}"}
            ]
          })
  
          font_size = kwargs.get("fontsize", DEFAULT_FONTSIZE)
  
          vega["marks"] = vega.get("marks", [])
          vega["marks"].append({
            "type": "text",
            "encode": {
              "enter": {
                "align": {"value": "center"},
                "baseline": {"value": "bottom"},
                "fill": {"value": "#333"},
                "fontSize": {"value": font_size}
              },
              "update": {
                "x": {"scale": "xscale", "signal": "(tooltip.x + tooltip.x2) / 2", "band": 0.5},
                "y": {"scale": "yscale", "signal": "tooltip.y", "offset": -2},
                "text": {"signal": "tooltip.y"},
                "fillOpacity": [
                  {"test": "datum === tooltip", "value": 0},
                  {"value": 1}
                ]
              }
            }
          })
docs: In one-dimensional plots, show values above the value on hover.