If you use :hover, :active, or other pseudo-classes in your CSS code, it can be tedious to test them. For example, having to hover over an element which is styled with the :hover pseudo-class means that you can't use your mouse to inspect the element in DevTools at the same time.
Thanks to DevTools, you can actually simulate these pseudo-classes without having to use your mouse or keyboard.
To simulate a pseudo-class:
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Inspect an element that has a pseudo-class defined in your CSS code. 
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Depending on your browser, do either of the following: - In Chrome, Edge, or Safari: in the Elements tool, in the Styles sidebar, click the :hovbutton.
- In Firefox: in the Inspector tool, in the Rules sidebar, click the :hovbutton.
- In Polypane: in the Elements tool, click the rhombus icon.
 The pseudo-class section appears. 
- In Chrome, Edge, or Safari: in the Elements tool, in the Styles sidebar, click the 
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Select one, or more, pseudo-classes to simulate. 
Here is a screencast showing how to use pseudo-class simulation to check the hover, active, visited and focused state of a link without having to interact with the link using your keyboard or mouse:
To try it out yourself, here is the demo page used in the video.