The close case button is very useful and handy when we want to close a case.
We don't need to provide much information to close a case.
The case is closed quickly with a related case comment created.
But at this very moment, Salesforce does not have a close case button in Lightning yet.
You can vote for the idea here: https://success.salesforce.com/ideaView?id=0873A000000cMWbQAM
Add a Close Case button in Lightning
If you want the close case function in Lightning now, we can create an action and add it to the case page layout.
Button, Links, and Actions-> Click
For Action Type, select
Update a Record,
For Standard Label Type, select
For Label, enter Close Case.
After clicking the Save button, create a Predefined Field Value and select
Edit the action page layout and drag the Internal Comments field to the page, remove the other fields and click Save.
Edit Case Page Layouts, drag the new quick action to the Salesforce Mobile and Lightning Experience Actions section, and Save.
Go to the case page and we can see the Close Case action.
Now we can use the Close Case function in Lightning without writing any code, isn't that cool?