style: Improve the styles for the separation in quick setting buttons

Sam Hewittrequested to merge
snwh/quick-settings-button-separation into main
  • remove the highlighting js in favour of color definitions, to fix it not really working in light theme or high contrast
  • add a bunch of color definitions to set the color of the menu button in the different styles
  • drop the border drawing for a separator, to fix visual issues with the high border radius, in favour of a separator element
  • change the class names of some things to make it understandable
  • bit of overall css tidying

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