To avoid having to scroll to and click in the Wikipedia search box when you want to use it, there is a keyboard shortcut to move the cursor there. Alt+⇧ Shift+F works on most PC systems. For an example of a search box in which the cursor is already focused, see the Wikipedia portal page.
On MacOS, press Ctrl+⇧ Shift+F instead of Alt+⇧ Shift+F.