changing the navigation colour for one item and different states

Hi there, I would like to change one of the colours of my navigation. I thought I could do this by adding in some code to my child style sheet but it does not work the code I added was:

#menu-item-118 a {
background:#7caece !important;
}

#menu-item-118 a:hover {
background: #7caece !important;
}

#menu-item-118 a:active {
background: #7caece !important;
}

The top bit of code does work so I can change the tab colour, but what do I need to do to change the hover colour and the selected item page colour. I am new to all this so any help you can give me would be much appreciated. Many thanks.