Please help on my Submenu style.

I want to have a background color for my sub menu when I hover my mouse on top of it.

This is my codes:
Hi guys, This is what I wanted to do.

1. When I hover my mouse on the sidemenu. It will change it background color.

Here is my codes.

#main-sidebar {
width: 185px;
float: left;
padding-right: 10px;
}
#article-sidebar {
color: #0b73b7;
font-size: 14px;
font-weight: bold;
}
#article-sidebar li {
padding-bottom: 15px;
}
#article-sidebar li ul {
padding: 5px 0px 0px 0px;
}
#article-sidebar li ul li {
padding: 7px 0px 0px 15px;
}
#article-sidebar a:link,
#article-sidebar a:visited,
#article-sidebar a:hover,
#article-sidebar a:active {
text-decoration: none;
}

But when I try to edit this one.

#article-sidebar a:link,
#article-sidebar a:visited,
#article-sidebar a:hover{
background-color: black;
}
#article-sidebar a:active {
text-decoration: none;
}

It changes the background color to black permanently..
I really appreciate all the replies.