Open the webpage in Safari, Chrome, or Firefox
Right-click the page and select Inspect or Inspect Element
On Safari, enable the Develop menu in Safari Settings or Preferences under Advanced
On Safari, use Option + Command + I after enabling the Develop menu
On Chrome, use Option + Command + I
On Firefox, use Option + Command + I
To inspect a specific item, right-click it and choose Inspect
To inspect on touchpad, use two-finger click or Control-click and select Inspect
To open the developer tools panel, use the browser menu and choose Developer Tools or Web Inspector