dotfiles/thunderbird/userChrome.css

* {
  box-shadow: none !important;
  border-radius: 0 !important;

  --selected-item-color: #9e9e9e !important;
  --selected-item-text-color: #212121 !important;

  --treeitem-background-active: #9e9e9e !important;

  --viewHighlightBorderColor: #9e9e9e !important;
  --viewHighlightTextColor: #212121 !important;
}

#folderTree .icon {
  --icon-color: #212121 !important;
}

.calendar-notification-bar {
  background-color: #f4f4f5 !important;
}

#calSidebar #primaryButtonSidePanel {
  display: none !important;
}

#tabs-toolbar {
  display: none;
}

.tab-line {
  display: none;
}