Active link not visible

Hi there,

I made a simple non-cms site for my employer ( www.grimach.nl). Now when I click a link in the main navigation bar, you can't see that the link is active.

I made the site in Dreamweaver with a template, where I attached some css-files to. Down here is the css-file I used for the main navigation.

/* ----------------------------------- */
/* Definition for mainNavigation-hover */
/* Active werkt nog niet*/
/* ----------------------------------- */
#mainNavigation a:hover, #mainNavigation a:active{
padding:0px;
margin:0px;
margin-left:auto;
margin-right:auto;

width:100%;
height:30px;

background-color:#FFF;
background-image:url(../images/mainbuttonRollover.png);

font-weight:bold;
text-transform:uppercase;

line-height:30px;

color: #fff;
}

#mainNavigation a:hover, #mainNavigation a:active {
padding:0px;
margin:0px;

}

#mainNavigation a:hover, #mainNavigation a:active{
margin:0px;
padding:0px;
width:100px;
float: left;

text-align:center;

display:inline;
}

Why can't the active link not be seen? Hope you can help me out. Thanks in advance.