When you’ve completed all the tasks in a list and want to remove it from the sidebar, you can archive it.
To archive, open your list, click
v beside the list name (above the list) to open the actions menu, and select "Archive."
You can also archive a list from the sidebar by clicking a smaller
v that appears as you hover your mouse above any list.
If at some point you want to restore this list to the sidebar along with your active lists, click "Archive" in your Favorites menu, and select your list.
Once in the list view, click
v beside the list name, and select "Restore List" from the popover menu.
In the next view, confirm the restoration and add the list back to your sidebar by clicking "Restore List".
Once the restored list is returned to the sidebar, you can start creating tasks in it again right away.
If you want to add this list to a group, you can do so using drag and drop.