title: Changing the background color of the selected options in a select box
body: <p><img src="https://i.stack.imgur.com/8Bdta.png" alt="enter image description here"></p>
  
  <p>I have to create a select box like this. I have been able to get this tree structure using optgroup but I am facing problems in changing the default background color of the selected option from default color to this orange color.
  I am aware of js solutions but I am more interested in pure HTML/CSS solution. It would be better if it will work in every browser, but no pressure ;)</p>
  
  <p>Thanks in advance.</p>