message: Fix broken pdf viewer with inverted color
  The fix is owed to
diff: @@ -259,8 +259,8 @@ function setupWebSocket() {
  }
  }
  if (data.invert > 0) {
  - document.querySelector('#viewer').style.filter = `invert(${data.invert * 100}%)`
  - document.querySelector('#viewer').style.background = 'white'
  + document.querySelector('html').style.filter = `invert(${data.invert * 100}%)`
  + document.querySelector('html').style.background = 'white'
  }
  if (data.keybindings) {
  reverseSynctexKeybinding = data.keybindings['synctex']
  