Border.symmetric constructor
      const
      Border.symmetric({ 
    
- BorderSide vertical = BorderSide.none,
- BorderSide horizontal = BorderSide.none,
Creates a border with symmetrical vertical and horizontal sides.
Implementation
const Border.symmetric({
  BorderSide vertical = BorderSide.none,
  BorderSide horizontal = BorderSide.none,
})  : left = vertical,
      top = horizontal,
      right = vertical,
      bottom = horizontal,
      super();