CSS3 Opacity - background only [duplicate]

Question

I wanted to change the opacity of my navigations background color but it also changed the opacity of the links of my navigation. How do I change the opacity of my navigations background color only?

This is my style for my navigaton:

#navigation { 
    height: 60px;
    width: auto;
    margin: 0 0 20px 0;
    background-color: black;
    border-radius: 8px;
    opacity: 0.7;
}

#navigation ul {
    list-style-type: none;
}

#navigation li {
    padding-left: 22px;
    float: left;
}

#navigation a {
    text-decoration: none;
    display: inline-block;
    float: left;
    padding: 10px 20px 10px 20px;
    color: white;
    margin-top: 10px;
    opacity: 1;
}

#navigation a:hover {
    background-color: orange;
    border-radius: 10px;
}

Answer 1

You can do it like this:

background-color: rgba(0,0,0,0.7);

this changes the background color of black opacity to 0.7 without effecting anything else