title: Plotly: How to edit unified hoverlabel?
body: <p>I am generating a graph with two different contour lines. When I hover the mouse over the graph it compares a menu with the values of the two contours as in the image:</p>
  
  <p><a href="https://i.stack.imgur.com/oSQex.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/oSQex.png" alt="enter image description here"></a></p>
  
  <p>I obtained this result with this code:</p>
  
  <pre><code># IMPORT
  import plotly.graph_objs as go
  import plotly.offline as pyo
  import numpy as np
  
  # CONSTANTS SET UP
  N = 11
  x_min = 0
  x_max = 10
  y_min = 0
  y_max = 10
  fontsize = 18
  
  # COLORS SET UP
  blue = '#6683f3'
  orange = '#ff9266'
  black = '#212121'
  
  # DEFINE THE MESH GRID
  x = np.linspace(x_min, x_max, N)
  y = np.linspace(y_min, y_max, N)
  XX, YY = np.meshgrid(x, y)
  
  # CALCULATE Z1 AND Z2
  Z1 = XX + YY
  Z2 = XX - YY
  
  # DEFINE THE TRACES LIST
  data = [go.Contour(z = Z1,
                     transpose = True,
                     name = 'Z1',
                     zmin = np.min(Z1),
                     zmax = np.max(Z1) + 1,
                     hovertemplate = 'Z1 = %{z: .0f}&lt;extra&gt;&lt;/extra&gt;',
                     contours_coloring = 'lines',
                     showscale = False,
                     showlegend = True,
                     colorscale = [[0, orange], [1, orange]],
                     line_width = 4,
                     ncontours = 20,
                     contours = dict(showlabels = True,
                                     labelformat = '.0f',
                                     labelfont = dict(size = 18))),
          go.Contour(z = Z2,
                     transpose = True,
                     name = 'Z2',
                     zmin = np.min(Z2),
                     zmax = np.max(Z2) + 1,
                     hovertemplate = 'Z2 = %{z: .0f}&lt;extra&gt;&lt;/extra&gt;',
                     contours_coloring = 'lines',
                     showscale = False,
                     showlegend = True,
                     colorscale = [[0, blue], [1, blue]],
                     line_width = 4,
                     ncontours = 20,
                     contours = dict(showlabels = True,
                                     labelformat = '.0f',
                                     labelfont = dict(size = fontsize)))]
  
  # DEFINE THE LAYOUT
  layout = go.Layout(plot_bgcolor = black,
                     hovermode = 'x')
  
  # DEFINE THE FIGURE
  figure = go.Figure(data = data,
                     layout = layout)
  
  # IMPROVE LEGEND AND HOVERLABEL ASPECT
  figure.update_layout(legend = dict(itemsizing = 'constant',
                                     font = dict(size = fontsize)),
                       hoverlabel = dict(font_size = fontsize))
  
  # PLOT THE FIGURE
  pyo.plot(figure)
  </code></pre>
  
  <p>In the layout definition section, if I replace <code>hovermode = 'x'</code> with <code>hovermode = 'x unified'</code> I get this result:</p>
  
  <p><a href="https://i.stack.imgur.com/GXzBt.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GXzBt.png" alt="enter image description here"></a></p>
  
  <p>I would like to remove from this menu the first line that contains the information on the x. I honestly don't know where to start, I tried to consult the <a href="https://plotly.com/python/reference/#layout-hovermode" rel="nofollow noreferrer">plotly documentation</a> but I did not get any clue.<br>
  What I would get (image manually edited):</p>
  
  <p><a href="https://i.stack.imgur.com/d0Plw.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/d0Plw.png" alt="enter image description here"></a></p>
  
  <p>A possible alternative would be to improve the appearance of the menu that appears in the first image:</p>
  
  <ul>
  <li>adding a unique background for the two contours</li>
  <li>adding a colored line for each contour</li>
  </ul>
  
  <p>Version info:</p>
  
  <pre><code>Python  4.7.0
  dash    1.12.0
  plotly  4.7.0
  </code></pre>