title: Change colors in python dash plotly theme
body: <p>I am currently creating my first plotly dash app and have a question on graph theming:</p>
  
  <p>I want to use the available <code>plotly_dark</code> theme and only adjust the underlying colors (background and element colors) to custom values. I played around with the ideas provided here: <a href="https://plotly.com/python/templates/#saving-and-distributing-custom-themes" rel="noreferrer">https://plotly.com/python/templates/#saving-and-distributing-custom-themes</a> like this</p>
  
  <pre><code>import plotly.graph_objects as go
  import plotly.io as pio
  
  pio.templates["plotly_dark_custom"] = go.layout.Template(
      ...custom definitions here...
  )
  pio.templates.default = "plotly_dark_custom"
  </code></pre>
  
  <p>but I was wondering if there is a more intuitive way, e.g. building a child theme from <code>plotly_dark</code>
  and only override the colors (providing a palette for the colors and define the new background color) afterwards. </p>
  
  <p>As I am very new to Python my knowledge here is very limited, so I hope you can give me some pointers in the right direction. </p>
  
  <p>Thank you and let me know if I should provide more details on this request.
  Stephan</p>