Place in your ~/.config/fish/functions folder. The "scroll" command will then toggle macOS/classic style scrollbars to help test websites.

scroll.fish

function scroll
  set state (defaults read NSGlobalDomain AppleShowScrollBars)

  if [ $state = "Automatic" ]
    set state "Always"
    echo "Scrollbars set to classic (always visible)"
  else
    set state "Automatic"
    echo "Scrollbars set to normal macOS (autohide, zero width)"
  end

  defaults write NSGlobalDomain AppleShowScrollBars -string $state

  # Finder has to restart (but not via the GUI for some reason)
  killall Finder

  # Chrome has to restart for the scrollbars to change :(
  if pgrep "Google Chrome" > /dev/null 
  and read -n 1 -p "set_color -o brblue; echo -n 'Restart Chrome [y,n]? '; set_color normal" yesno
  and [ $yesno = "y" ]
    osascript -e 'tell app "Google Chrome" to quit'
    sleep 1
    open -a "Google Chrome"
  end
end