Inspect Element of macOS system App

I bet you know serveral native Apps on macOS is written in HTML.

Use these commands:

defaults write NSGlobalDomain WebKitDeveloperExtras -bool true
defaults write -g WebKitDeveloperExtras -bool YES

1

Open WebKitDeveloperExtras

Open your terminal and execute the two shell commands above.

2

Check element of macOS "native" Apps

Right click on a "native" App and select "Inspect Element".