Set background color of a <div> element when the <div> element or any child elements get focus:
The focusin event occurs when an element (or any elements inside it) gets focus.
The focusin() method attaches a function to run when a focus event occurs on the element, or any elements inside it.
Unlike the focus() method, the focusin() method also triggers if any child elements get focus.
Tip: An element gets focus when selected by a mouse click or by "tab-navigating" to it.
Tip: This method is often used together with the focusout() method.
|function||Required. Specifies the function to run when the focusin event occurs.|