how to get iframe parent html and change css

Question

I have some pages with iframe, inside the iframe have navigation bar with onmouseover and act.. when the navigation bar is open displaying scroll bar, but I don't wont that, so i increased the height of the frame height 300px.

here by problem.. i can not press on buttons under the iframe.

i try to play with the z-index and with div wrapper and nothing help. please try to help me.. thank's.

<div id="navStyle" onmouseover... onmouseout... >
<iframe id="navigation" src="navigation.html" frameborder="0" </iframe>
</div>

#navigation{
    position:absolute;
    width: 1150px;
    height:300px;
    margin-top:0px;
    padding-top:0px;
    border: 0px 0px 0px 0px;
    z-index:-1;
    clear: both;
}

#navStyle{
    z-index:0;
    clear: both;
    height:10px;
}

thats just one from many options i try.