I can not to change the appearance (color status:link, visited, hover, active) links using CSS.

My code in "style1.css"

a {
font-weight: bold;
}

a : link {
color: black;
}

a : visited {
color: gray;
}

a : hover {
text-decoration: none;
color: white;
background-color: navy;
}

a : active {
color: aqua;
background-color: navy;
}


Thanks in advance for the help!