history-backward hover color

Hello.

I use

#ui-bar-toggle:hover{
background-color: purple
}

and that changes toggle button color to purple when mouse is over it.

However neither

#history-backward: hover {
background-color: purple
}

nor

#menu-item-saves:hover{
background-color: purple
}

does not change color of buttons when mouse is over it.

What do I do wrong and how to do it right?