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.nav-tab {
  ...
  // instead of putting it on
  border-right: 1px solid #424242;
  &:last-child {
    border-right: 0; // and then taking it off
  }
  // use CSS not() to only apply to the elements you want
  &:not(:last-child) {
    border-right: 1px solid #424242;
  }
  ...
}